Hi

Am 13.07.21 um 22:51 schrieb Daniel Vetter:

tldr; DMA buffers aren't normal memory, expecting that you can use them like that (like calling get_user_pages works, or that they're accounting like any other normal memory) cannot be guaranteed.

Since some userspace only runs on integrated devices, where all buffers are actually all resident system memory, there's a huge temptation to assume that a struct page is always present and useable like for any more pagecache backed mmap. This has the potential to result in a uapi nightmare.

To stop this gap require that DMA buffer mmaps are VM_PFNMAP, which blocks get_user_pages and all the other struct page based infrastructure for everyone. In spirit this is the uapi counterpart to the kernel-internal CONFIG_DMABUF_DEBUG.

Motivated by a recent patch which wanted to swich the system dma-buf heap to vm_insert_page instead of vm_insert_pfn.

v2:

Jason brought up that we also want to guarantee that all ptes have the pte_special flag set, to catch fast get_user_pages (on architectures that support this). Allowing VM_MIXEDMAP (like VM_SPECIAL does) would still allow vm_insert_page, but limiting to VM_PFNMAP will catch that.

From auditing the various functions to insert pfn pte entires (vm_insert_pfn_prot, remap_pfn_range and all it's callers like dma_mmap_wc) it looks like VM_PFNMAP is already required anyway, so this should be the correct flag to check for.

References: https://lore.kernel.org/lkml/CAKMK7uHi+mG0z0HUmNt13QCCvutuRVjpcR0NjRL12k-WbW... Acked-by: Christian König christian.koenig@amd.com Cc: Jason Gunthorpe jgg@ziepe.ca Cc: Suren Baghdasaryan surenb@google.com Cc: Matthew Wilcox willy@infradead.org Cc: John Stultz john.stultz@linaro.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org -- Resending this so I can test the next two patches for vgem/shmem in intel-gfx-ci. Last round failed somehow, but I can't repro that at all locally here.

No immediate plans to merge this patch here since ttm isn't addressed yet (and there we have the hugepte issue, for which I don't think we have a clear consensus yet).

-Daniel

drivers/dma-buf/dma-buf.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 510b42771974..65cbd7f0f16a 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -130,6 +130,7 @@ static struct file_system_type dma_buf_fs_type = { static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma) { struct dma_buf *dmabuf;

• int ret;

  if (!is_dma_buf_file(file)) return -EINVAL;

@@ -145,7 +146,11 @@ static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma) dmabuf->size >> PAGE_SHIFT) return -EINVAL;

• return dmabuf->ops->mmap(dmabuf, vma);

• ret = dmabuf->ops->mmap(dmabuf, vma);
• WARN_ON(!(vma->vm_flags & VM_PFNMAP));

Maybe change this to WARN_ON_ONCE(), so it doesn't fill up the kernel log. Same comment below.

For either version

Acked-by: Thomas Zimmermann tzimmermann@suse.de

Best regards Thomas

• return ret; }

  static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)

@@ -1276,6 +1281,8 @@ EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access); int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma, unsigned long pgoff) {

• int ret;
• if (WARN_ON(!dmabuf || !vma)) return -EINVAL;

@@ -1296,7 +1303,11 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma, vma_set_file(vma, dmabuf->file); vma->vm_pgoff = pgoff;

• return dmabuf->ops->mmap(dmabuf, vma);

• ret = dmabuf->ops->mmap(dmabuf, vma);
• WARN_ON(!(vma->vm_flags & VM_PFNMAP));
• return ret; } EXPORT_SYMBOL_GPL(dma_buf_mmap);

Hi,

I'm not knowledgeable enougth to give this a full review. If you can just answer my questions, fell free to add an

Acked-by: Thomas Zimmermann tzimmermann@suse.de

to the patch. :)

Am 13.07.21 um 22:51 schrieb Daniel Vetter:

We want to stop gup, which isn't the case if we use vmf_insert_page

What is gup?

and VM_MIXEDMAP, because that does not set pte_special.

v2: With this shmem gem helpers now definitely need CONFIG_MMU (0day)

v3: add more depends on MMU. For usb drivers this is a bit awkward, but really it's correct: To be able to provide a contig mapping of buffers to userspace on !MMU platforms we'd need to use the cma helpers for these drivers on those platforms. As-is this wont work.

Also not exactly sure why vm_insert_page doesn't go boom, because that definitely wont fly in practice since the pages are non-contig to begin with.

Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch

---

drivers/gpu/drm/Kconfig | 2 +- drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++-- drivers/gpu/drm/gud/Kconfig | 2 +- drivers/gpu/drm/tiny/Kconfig | 4 ++-- drivers/gpu/drm/udl/Kconfig | 1 + 5 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 0d372354c2d0..314eefa39892 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -211,7 +211,7 @@ config DRM_KMS_CMA_HELPER

config DRM_GEM_SHMEM_HELPER bool

• depends on DRM

• depends on DRM && MMU help Choose this if you need the GEM shmem helper functions

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index d5e6d4568f99..296ab1b7c07f 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -542,7 +542,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) } else { page = shmem->pages[page_offset];

• ret = vmf_insert_page(vma, vmf->address, page);
  

• ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
  

  }

  mutex_unlock(&shmem->pages_lock);

@@ -612,7 +612,7 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) return ret; }

• vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;

• vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND; vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); if (shmem->map_wc) vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);

diff --git a/drivers/gpu/drm/gud/Kconfig b/drivers/gpu/drm/gud/Kconfig index 1c8601bf4d91..9c1e61f9eec3 100644 --- a/drivers/gpu/drm/gud/Kconfig +++ b/drivers/gpu/drm/gud/Kconfig @@ -2,7 +2,7 @@

config DRM_GUD tristate "GUD USB Display"

• depends on DRM && USB

• depends on DRM && USB && MMU select LZ4_COMPRESS select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER

I'm a kconfig noob, so this is rather a question than a review comment:

If DRM_GEM_SHMEM_HELPER already depends on MMU, this select will fail on non-MMU platforms? Why does the driver also depend on MMU? Simply to make the item disappear in menuconfig?

Best regards Thomas

diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig index 5593128eeff9..c11fb5be7d09 100644 --- a/drivers/gpu/drm/tiny/Kconfig +++ b/drivers/gpu/drm/tiny/Kconfig @@ -44,7 +44,7 @@ config DRM_CIRRUS_QEMU

config DRM_GM12U320 tristate "GM12U320 driver for USB projectors"

• depends on DRM && USB

• depends on DRM && USB && MMU select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER help

@@ -53,7 +53,7 @@ config DRM_GM12U320

config DRM_SIMPLEDRM tristate "Simple framebuffer driver"

• depends on DRM

• depends on DRM && MMU select DRM_GEM_SHMEM_HELPER select DRM_KMS_HELPER help

diff --git a/drivers/gpu/drm/udl/Kconfig b/drivers/gpu/drm/udl/Kconfig index 1f497d8f1ae5..c744175c6992 100644 --- a/drivers/gpu/drm/udl/Kconfig +++ b/drivers/gpu/drm/udl/Kconfig @@ -4,6 +4,7 @@ config DRM_UDL depends on DRM depends on USB depends on USB_ARCH_HAS_HCD

• depends on MMU select DRM_GEM_SHMEM_HELPER select DRM_KMS_HELPER help

On Thu, Jul 22, 2021 at 08:22:43PM +0200, Thomas Zimmermann wrote:

Hi,

I'm not knowledgeable enougth to give this a full review. If you can just answer my questions, fell free to add an

Acked-by: Thomas Zimmermann tzimmermann@suse.de

to the patch. :)

Am 13.07.21 um 22:51 schrieb Daniel Vetter:

...

We want to stop gup, which isn't the case if we use vmf_insert_page

What is gup?

...

and VM_MIXEDMAP, because that does not set pte_special.

v2: With this shmem gem helpers now definitely need CONFIG_MMU (0day)

v3: add more depends on MMU. For usb drivers this is a bit awkward, but really it's correct: To be able to provide a contig mapping of buffers to userspace on !MMU platforms we'd need to use the cma helpers for these drivers on those platforms. As-is this wont work.

Also not exactly sure why vm_insert_page doesn't go boom, because that definitely wont fly in practice since the pages are non-contig to begin with.

Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch

---

drivers/gpu/drm/Kconfig | 2 +- drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++-- drivers/gpu/drm/gud/Kconfig | 2 +- drivers/gpu/drm/tiny/Kconfig | 4 ++-- drivers/gpu/drm/udl/Kconfig | 1 + 5 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 0d372354c2d0..314eefa39892 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -211,7 +211,7 @@ config DRM_KMS_CMA_HELPER config DRM_GEM_SHMEM_HELPER bool

• depends on DRM

• depends on DRM && MMU help Choose this if you need the GEM shmem helper functions

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index d5e6d4568f99..296ab1b7c07f 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -542,7 +542,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) } else { page = shmem->pages[page_offset];

• ret = vmf_insert_page(vma, vmf->address, page);
  

• ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
  

  } mutex_unlock(&shmem->pages_lock);

@@ -612,7 +612,7 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) return ret; }

• vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;

• vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND; vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); if (shmem->map_wc) vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);

diff --git a/drivers/gpu/drm/gud/Kconfig b/drivers/gpu/drm/gud/Kconfig index 1c8601bf4d91..9c1e61f9eec3 100644 --- a/drivers/gpu/drm/gud/Kconfig +++ b/drivers/gpu/drm/gud/Kconfig @@ -2,7 +2,7 @@ config DRM_GUD tristate "GUD USB Display"

• depends on DRM && USB

• depends on DRM && USB && MMU select LZ4_COMPRESS select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER

I'm a kconfig noob, so this is rather a question than a review comment:

If DRM_GEM_SHMEM_HELPER already depends on MMU, this select will fail on non-MMU platforms? Why does the driver also depend on MMU? Simply to make the item disappear in menuconfig?

I totally missed this somehow. vmf_insert_pfn functions only exists for MMU based system. So we can't compile vgem without that. And yes it just makes it disappear.

tbh I'm not sure it even worked with the old code, because on !MMU platforms it's the mmap's implementation job to make sure the pages are physically contiguous. There's another mmap related callback which should return the physical address where the memory starts.

The cma helpers otoh should work on !MMU platforms, because they will give us a physically contig memory region. -Daniel

Best regards Thomas

...

diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig index 5593128eeff9..c11fb5be7d09 100644 --- a/drivers/gpu/drm/tiny/Kconfig +++ b/drivers/gpu/drm/tiny/Kconfig @@ -44,7 +44,7 @@ config DRM_CIRRUS_QEMU config DRM_GM12U320 tristate "GM12U320 driver for USB projectors"

• depends on DRM && USB

• depends on DRM && USB && MMU select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER help

@@ -53,7 +53,7 @@ config DRM_GM12U320 config DRM_SIMPLEDRM tristate "Simple framebuffer driver"

• depends on DRM

• depends on DRM && MMU select DRM_GEM_SHMEM_HELPER select DRM_KMS_HELPER help

diff --git a/drivers/gpu/drm/udl/Kconfig b/drivers/gpu/drm/udl/Kconfig index 1f497d8f1ae5..c744175c6992 100644 --- a/drivers/gpu/drm/udl/Kconfig +++ b/drivers/gpu/drm/udl/Kconfig @@ -4,6 +4,7 @@ config DRM_UDL depends on DRM depends on USB depends on USB_ARCH_HAS_HCD

• depends on MMU select DRM_GEM_SHMEM_HELPER select DRM_KMS_HELPER help

-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer

Am 13.07.21 um 22:51 schrieb Daniel Vetter:

intel-gfx-ci realized that something is not quite coherent anymore on some platforms for our i915+vgem tests, when I tried to switch vgem over to shmem helpers.

After lots of head-scratching I realized that I've removed calls to drm_clflush. And we need those. To make this a bit cleaner use the same page allocation tooling as ttm, which does internally clflush (and more, as neeeded on any platform instead of just the intel x86 cpus i915 can be combined with).

Unfortunately this doesn't exist on arm, or as a generic feature. For that I think only the dma-api can get at wc memory reliably, so maybe we'd need some kind of GFP_WC flag to do this properly.

The problem is that this stuff is extremely architecture specific. So GFP_WC and GFP_UNCACHED are really what we should aim for in the long term.

And as far as I know we have at least the following possibilities how it is implemented:

* A fixed amount of registers which tells the CPU the caching behavior for a memory region, e.g. MTRR. * Some bits of the memory pointers used, e.g. you see the same memory at different locations with different caching attributes. * Some bits in the CPUs page table. * Some bits in a separate page table.

On top of that there is the PCIe specification which defines non-cache snooping access as an extension.

Mixing that with the CPU caching behavior gets you some really nice ways to break a driver. In general x86 seems to be rather graceful, but arm and PowerPC are easily pissed if you mess that up.

Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Christian König christian.koenig@amd.com Cc: "Thomas Hellström" thomas.hellstrom@linux.intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch

Acked-by: Christian könig christian.koenig@amd.com

Regards, Christian.

---

drivers/gpu/drm/drm_gem_shmem_helper.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 296ab1b7c07f..657d2490aaa5 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -10,6 +10,10 @@ #include <linux/slab.h> #include <linux/vmalloc.h>

+#ifdef CONFIG_X86 +#include <asm/set_memory.h> +#endif

• #include <drm/drm.h> #include <drm/drm_device.h> #include <drm/drm_drv.h>

@@ -162,6 +166,11 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) return PTR_ERR(pages); }

+#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wc(pages, obj->size >> PAGE_SHIFT);
  

+#endif

• shmem->pages = pages;

  return 0;

@@ -203,6 +212,11 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) if (--shmem->pages_use_count > 0) return;

+#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
  

+#endif

• drm_gem_put_pages(obj, shmem->pages, shmem->pages_mark_dirty_on_put, shmem->pages_mark_accessed_on_put);

Am 14.07.21 um 14:48 schrieb Daniel Vetter:

On Wed, Jul 14, 2021 at 01:54:50PM +0200, Christian König wrote:

...

Am 13.07.21 um 22:51 schrieb Daniel Vetter:

...

intel-gfx-ci realized that something is not quite coherent anymore on some platforms for our i915+vgem tests, when I tried to switch vgem over to shmem helpers.

After lots of head-scratching I realized that I've removed calls to drm_clflush. And we need those. To make this a bit cleaner use the same page allocation tooling as ttm, which does internally clflush (and more, as neeeded on any platform instead of just the intel x86 cpus i915 can be combined with).

Unfortunately this doesn't exist on arm, or as a generic feature. For that I think only the dma-api can get at wc memory reliably, so maybe we'd need some kind of GFP_WC flag to do this properly.

The problem is that this stuff is extremely architecture specific. So GFP_WC and GFP_UNCACHED are really what we should aim for in the long term.

And as far as I know we have at least the following possibilities how it is implemented:

• A fixed amount of registers which tells the CPU the caching behavior for a

memory region, e.g. MTRR.

• Some bits of the memory pointers used, e.g. you see the same memory at

different locations with different caching attributes.

• Some bits in the CPUs page table.
• Some bits in a separate page table.

On top of that there is the PCIe specification which defines non-cache snooping access as an extension.

Yeah dma-buf is extremely ill-defined even on x86 if you combine these all. We just play a game of whack-a-mole with the cacheline dirt until it's gone.

That's the other piece here, how do you even make sure that the page is properly flushed and ready for wc access:

• easy case is x86 with clflush available pretty much everywhere (since 10+ years at least)
• next are cpus which have some cache flush instructions, but it's highly cpu model specific
• next up is the same, but you absolutely have to make sure there's no other mapping around anymore or the coherency fabric just dies
• and I'm pretty sure there's worse stuff where you defacto can only allocate wc memory that's set aside at boot-up and that's all you ever get.

Well long story short you don't make sure that the page is flushed at all.

What you do is to allocate the page as WC in the first place, if you fail to do this you can't use it.

The whole idea TTM try to sell until a while ago that you can actually change that on the fly only works on x86 and even there only very very limited.

Cheers, Christian.

Cheers, Daniel

...

Mixing that with the CPU caching behavior gets you some really nice ways to break a driver. In general x86 seems to be rather graceful, but arm and PowerPC are easily pissed if you mess that up.

...

Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Christian König christian.koenig@amd.com Cc: "Thomas Hellström" thomas.hellstrom@linux.intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch

Acked-by: Christian könig christian.koenig@amd.com

Regards, Christian.

...

---

drivers/gpu/drm/drm_gem_shmem_helper.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 296ab1b7c07f..657d2490aaa5 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -10,6 +10,10 @@ #include <linux/slab.h> #include <linux/vmalloc.h> +#ifdef CONFIG_X86 +#include <asm/set_memory.h> +#endif

• #include <drm/drm.h> #include <drm/drm_device.h> #include <drm/drm_drv.h>

@@ -162,6 +166,11 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) return PTR_ERR(pages); } +#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wc(pages, obj->size >> PAGE_SHIFT);
  

+#endif

• shmem->pages = pages; return 0;

@@ -203,6 +212,11 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) if (--shmem->pages_use_count > 0) return; +#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
  

+#endif

• drm_gem_put_pages(obj, shmem->pages, shmem->pages_mark_dirty_on_put, shmem->pages_mark_accessed_on_put);

Hi

Am 13.07.21 um 22:51 schrieb Daniel Vetter:

intel-gfx-ci realized that something is not quite coherent anymore on some platforms for our i915+vgem tests, when I tried to switch vgem over to shmem helpers.

After lots of head-scratching I realized that I've removed calls to drm_clflush. And we need those. To make this a bit cleaner use the same page allocation tooling as ttm, which does internally clflush (and more, as neeeded on any platform instead of just the intel x86 cpus i915 can be combined with).

Vgem would therefore not work correctly on non-X86 platforms?

Unfortunately this doesn't exist on arm, or as a generic feature. For that I think only the dma-api can get at wc memory reliably, so maybe we'd need some kind of GFP_WC flag to do this properly.

Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Christian König christian.koenig@amd.com Cc: "Thomas Hellström" thomas.hellstrom@linux.intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch

---

drivers/gpu/drm/drm_gem_shmem_helper.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 296ab1b7c07f..657d2490aaa5 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -10,6 +10,10 @@ #include <linux/slab.h> #include <linux/vmalloc.h>

+#ifdef CONFIG_X86 +#include <asm/set_memory.h> +#endif

• #include <drm/drm.h> #include <drm/drm_device.h> #include <drm/drm_drv.h>

@@ -162,6 +166,11 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) return PTR_ERR(pages); }

+#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wc(pages, obj->size >> PAGE_SHIFT);
  

+#endif

I cannot comment much on the technical details of the caching of various architectures. If this patch goes in, there should be a longer comment that reflects the discussion in this thread. It's apparently a workaround.

I think the call itself should be hidden behind a DRM API, which depends on CONFIG_X86. Something simple like

ifdef CONFIG_X86 drm_set_pages_array_wc() { set_pages_array_wc(); } else drm_set_pages_array_wc() { } #endif

Maybe in drm_cache.h?

Best regard Thomas

• shmem->pages = pages;

  return 0;

@@ -203,6 +212,11 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) if (--shmem->pages_use_count > 0) return;

+#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
  

+#endif

• drm_gem_put_pages(obj, shmem->pages, shmem->pages_mark_dirty_on_put, shmem->pages_mark_accessed_on_put);

Am 23.07.21 um 09:36 schrieb Daniel Vetter:

On Thu, Jul 22, 2021 at 08:40:56PM +0200, Thomas Zimmermann wrote:

...

Hi

Am 13.07.21 um 22:51 schrieb Daniel Vetter: [SNIP]

...

+#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wc(pages, obj->size >> PAGE_SHIFT);
  

+#endif

I cannot comment much on the technical details of the caching of various architectures. If this patch goes in, there should be a longer comment that reflects the discussion in this thread. It's apparently a workaround.

I think the call itself should be hidden behind a DRM API, which depends on CONFIG_X86. Something simple like

ifdef CONFIG_X86 drm_set_pages_array_wc() { set_pages_array_wc(); } else drm_set_pages_array_wc() { } #endif

Maybe in drm_cache.h?

We do have a bunch of this in drm_cache.h already, and architecture maintainers hate us for it.

Yeah, for good reasons :)

The real fix is to get at the architecture-specific wc allocator, which is currently not something that's exposed, but hidden within the dma api. I think having this stick out like this is better than hiding it behind fake generic code (like we do with drm_clflush, which defacto also only really works on x86).

The DMA API also doesn't really touch that stuff as far as I know.

What we rather do on other architectures is to set the appropriate caching flags on the CPU mappings, see function ttm_prot_from_caching().

Also note that ttm has the exact same ifdef in its page allocator, but it does fall back to using dma_alloc_coherent on other platforms.

This works surprisingly well on non x86 architectures as well. We just don't necessary update the kernel mappings everywhere which limits the kmap usage.

In other words radeon and nouveau still work on PowerPC AGP systems as far as I know for example.

Christian.

-Daniel

...

Best regard Thomas

...

• shmem->pages = pages; return 0;

@@ -203,6 +212,11 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) if (--shmem->pages_use_count > 0) return; +#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
  

+#endif

• drm_gem_put_pages(obj, shmem->pages, shmem->pages_mark_dirty_on_put, shmem->pages_mark_accessed_on_put);

-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer

Hi

Am 23.07.21 um 09:36 schrieb Daniel Vetter:

The real fix is to get at the architecture-specific wc allocator, which is currently not something that's exposed, but hidden within the dma api. I think having this stick out like this is better than hiding it behind fake generic code (like we do with drm_clflush, which defacto also only really works on x86).

Also note that ttm has the exact same ifdef in its page allocator, but it does fall back to using dma_alloc_coherent on other platforms.

If this fixes a real problem and there's no full solution yet, let's take what we have. So if you can extract the essence of this comment into a TODO comment that tells how to fix the issue, fell free to add my

Acked-by: Thomas Zimmermann tzimmermann@suse.de

Best regards Thomas

-Daniel

...

Best regard Thomas

...

• shmem->pages = pages; return 0;

@@ -203,6 +212,11 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) if (--shmem->pages_use_count > 0) return; +#ifdef CONFIG_X86

• if (shmem->map_wc)

• set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
  

+#endif

• drm_gem_put_pages(obj, shmem->pages, shmem->pages_mark_dirty_on_put, shmem->pages_mark_accessed_on_put);

-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer

Aside from deleting lots of code the real motivation here is to switch the mmap over to VM_PFNMAP, to be more consistent with what real gpu drivers do. They're all VM_PFNMP, which means get_user_pages doesn't work, and even if you try and there's a struct page behind that, touching it and mucking around with its refcount can upset drivers real bad.

v2: Review from Thomas: - sort #include - drop more dead code that I didn't spot somehow

v3: select DRM_GEM_SHMEM_HELPER to make it build (intel-gfx-ci)

v4: I got tricked by 0cf2ef46c6c0 ("drm/shmem-helper: Use cached mappings by default"), and we need WC in vgem because vgem doesn't have explicit begin/end cpu access ioctls.

Also add a comment why exactly vgem has to use wc.

v5: Don't set obj->base.funcs, it will default to drm_gem_shmem_funcs (Thomas)

v6: vgem also needs an MMU for remapping

v7: I absolutely butchered the rebases over the vgem mmap change and revert and broke the patch. Actually go back to v6 from before the vgem mmap changes.

Cc: Thomas Zimmermann tzimmermann@suse.de Acked-by: Thomas Zimmermann tzimmermann@suse.de Cc: John Stultz john.stultz@linaro.org Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Melissa Wen melissa.srw@gmail.com Cc: Chris Wilson chris@chris-wilson.co.uk --- drivers/gpu/drm/Kconfig | 5 +- drivers/gpu/drm/vgem/vgem_drv.c | 342 ++------------------------------ 2 files changed, 16 insertions(+), 331 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 314eefa39892..28f7d2006e8b 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -272,7 +272,8 @@ source "drivers/gpu/drm/kmb/Kconfig"

config DRM_VGEM tristate "Virtual GEM provider" - depends on DRM + depends on DRM && MMU + select DRM_GEM_SHMEM_HELPER help Choose this option to get a virtual graphics memory manager, as used by Mesa's software renderer for enhanced performance. @@ -280,7 +281,7 @@ config DRM_VGEM

config DRM_VKMS tristate "Virtual KMS (EXPERIMENTAL)" - depends on DRM + depends on DRM && MMU select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER select CRC32 diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c index bf38a7e319d1..a87eafa89e9f 100644 --- a/drivers/gpu/drm/vgem/vgem_drv.c +++ b/drivers/gpu/drm/vgem/vgem_drv.c @@ -38,6 +38,7 @@

#include <drm/drm_drv.h> #include <drm/drm_file.h> +#include <drm/drm_gem_shmem_helper.h> #include <drm/drm_ioctl.h> #include <drm/drm_managed.h> #include <drm/drm_prime.h> @@ -50,87 +51,11 @@ #define DRIVER_MAJOR 1 #define DRIVER_MINOR 0

-static const struct drm_gem_object_funcs vgem_gem_object_funcs; - static struct vgem_device { struct drm_device drm; struct platform_device *platform; } *vgem_device;

-static void vgem_gem_free_object(struct drm_gem_object *obj) -{ - struct drm_vgem_gem_object *vgem_obj = to_vgem_bo(obj); - - kvfree(vgem_obj->pages); - mutex_destroy(&vgem_obj->pages_lock); - - if (obj->import_attach) - drm_prime_gem_destroy(obj, vgem_obj->table); - - drm_gem_object_release(obj); - kfree(vgem_obj); -} - -static vm_fault_t vgem_gem_fault(struct vm_fault *vmf) -{ - struct vm_area_struct *vma = vmf->vma; - struct drm_vgem_gem_object *obj = vma->vm_private_data; - /* We don't use vmf->pgoff since that has the fake offset */ - unsigned long vaddr = vmf->address; - vm_fault_t ret = VM_FAULT_SIGBUS; - loff_t num_pages; - pgoff_t page_offset; - page_offset = (vaddr - vma->vm_start) >> PAGE_SHIFT; - - num_pages = DIV_ROUND_UP(obj->base.size, PAGE_SIZE); - - if (page_offset >= num_pages) - return VM_FAULT_SIGBUS; - - mutex_lock(&obj->pages_lock); - if (obj->pages) { - get_page(obj->pages[page_offset]); - vmf->page = obj->pages[page_offset]; - ret = 0; - } - mutex_unlock(&obj->pages_lock); - if (ret) { - struct page *page; - - page = shmem_read_mapping_page( - file_inode(obj->base.filp)->i_mapping, - page_offset); - if (!IS_ERR(page)) { - vmf->page = page; - ret = 0; - } else switch (PTR_ERR(page)) { - case -ENOSPC: - case -ENOMEM: - ret = VM_FAULT_OOM; - break; - case -EBUSY: - ret = VM_FAULT_RETRY; - break; - case -EFAULT: - case -EINVAL: - ret = VM_FAULT_SIGBUS; - break; - default: - WARN_ON(PTR_ERR(page)); - ret = VM_FAULT_SIGBUS; - break; - } - - } - return ret; -} - -static const struct vm_operations_struct vgem_gem_vm_ops = { - .fault = vgem_gem_fault, - .open = drm_gem_vm_open, - .close = drm_gem_vm_close, -}; - static int vgem_open(struct drm_device *dev, struct drm_file *file) { struct vgem_file *vfile; @@ -159,266 +84,30 @@ static void vgem_postclose(struct drm_device *dev, struct drm_file *file) kfree(vfile); }

-static struct drm_vgem_gem_object *__vgem_gem_create(struct drm_device *dev, - unsigned long size) -{ - struct drm_vgem_gem_object *obj; - int ret; - - obj = kzalloc(sizeof(*obj), GFP_KERNEL); - if (!obj) - return ERR_PTR(-ENOMEM); - - obj->base.funcs = &vgem_gem_object_funcs; - - ret = drm_gem_object_init(dev, &obj->base, roundup(size, PAGE_SIZE)); - if (ret) { - kfree(obj); - return ERR_PTR(ret); - } - - mutex_init(&obj->pages_lock); - - return obj; -} - -static void __vgem_gem_destroy(struct drm_vgem_gem_object *obj) -{ - drm_gem_object_release(&obj->base); - kfree(obj); -} - -static struct drm_gem_object *vgem_gem_create(struct drm_device *dev, - struct drm_file *file, - unsigned int *handle, - unsigned long size) -{ - struct drm_vgem_gem_object *obj; - int ret; - - obj = __vgem_gem_create(dev, size); - if (IS_ERR(obj)) - return ERR_CAST(obj); - - ret = drm_gem_handle_create(file, &obj->base, handle); - if (ret) { - drm_gem_object_put(&obj->base); - return ERR_PTR(ret); - } - - return &obj->base; -} - -static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev, - struct drm_mode_create_dumb *args) -{ - struct drm_gem_object *gem_object; - u64 pitch, size; - - pitch = args->width * DIV_ROUND_UP(args->bpp, 8); - size = args->height * pitch; - if (size == 0) - return -EINVAL; - - gem_object = vgem_gem_create(dev, file, &args->handle, size); - if (IS_ERR(gem_object)) - return PTR_ERR(gem_object); - - args->size = gem_object->size; - args->pitch = pitch; - - drm_gem_object_put(gem_object); - - DRM_DEBUG("Created object of size %llu\n", args->size); - - return 0; -} - static struct drm_ioctl_desc vgem_ioctls[] = { DRM_IOCTL_DEF_DRV(VGEM_FENCE_ATTACH, vgem_fence_attach_ioctl, DRM_RENDER_ALLOW), DRM_IOCTL_DEF_DRV(VGEM_FENCE_SIGNAL, vgem_fence_signal_ioctl, DRM_RENDER_ALLOW), };

-static int vgem_mmap(struct file *filp, struct vm_area_struct *vma) -{ - unsigned long flags = vma->vm_flags; - int ret; - - ret = drm_gem_mmap(filp, vma); - if (ret) - return ret; - - /* Keep the WC mmaping set by drm_gem_mmap() but our pages - * are ordinary and not special. - */ - vma->vm_flags = flags | VM_DONTEXPAND | VM_DONTDUMP; - return 0; -} +DEFINE_DRM_GEM_FOPS(vgem_driver_fops);

-static const struct file_operations vgem_driver_fops = { - .owner = THIS_MODULE, - .open = drm_open, - .mmap = vgem_mmap, - .poll = drm_poll, - .read = drm_read, - .unlocked_ioctl = drm_ioctl, - .compat_ioctl = drm_compat_ioctl, - .release = drm_release, -}; - -static struct page **vgem_pin_pages(struct drm_vgem_gem_object *bo) -{ - mutex_lock(&bo->pages_lock); - if (bo->pages_pin_count++ == 0) { - struct page **pages; - - pages = drm_gem_get_pages(&bo->base); - if (IS_ERR(pages)) { - bo->pages_pin_count--; - mutex_unlock(&bo->pages_lock); - return pages; - } - - bo->pages = pages; - } - mutex_unlock(&bo->pages_lock); - - return bo->pages; -} - -static void vgem_unpin_pages(struct drm_vgem_gem_object *bo) -{ - mutex_lock(&bo->pages_lock); - if (--bo->pages_pin_count == 0) { - drm_gem_put_pages(&bo->base, bo->pages, true, true); - bo->pages = NULL; - } - mutex_unlock(&bo->pages_lock); -} - -static int vgem_prime_pin(struct drm_gem_object *obj) +static struct drm_gem_object *vgem_gem_create_object(struct drm_device *dev, size_t size) { - struct drm_vgem_gem_object *bo = to_vgem_bo(obj); - long n_pages = obj->size >> PAGE_SHIFT; - struct page **pages; + struct drm_gem_shmem_object *obj;

- pages = vgem_pin_pages(bo); - if (IS_ERR(pages)) - return PTR_ERR(pages); + obj = kzalloc(sizeof(*obj), GFP_KERNEL); + if (!obj) + return NULL;

- /* Flush the object from the CPU cache so that importers can rely - * on coherent indirect access via the exported dma-address. + /* + * vgem doesn't have any begin/end cpu access ioctls, therefore must use + * coherent memory or dma-buf sharing just wont work. */ - drm_clflush_pages(pages, n_pages); - - return 0; -} - -static void vgem_prime_unpin(struct drm_gem_object *obj) -{ - struct drm_vgem_gem_object *bo = to_vgem_bo(obj); - - vgem_unpin_pages(bo); -} - -static struct sg_table *vgem_prime_get_sg_table(struct drm_gem_object *obj) -{ - struct drm_vgem_gem_object *bo = to_vgem_bo(obj); - - return drm_prime_pages_to_sg(obj->dev, bo->pages, bo->base.size >> PAGE_SHIFT); -} - -static struct drm_gem_object* vgem_prime_import(struct drm_device *dev, - struct dma_buf *dma_buf) -{ - struct vgem_device *vgem = container_of(dev, typeof(*vgem), drm); - - return drm_gem_prime_import_dev(dev, dma_buf, &vgem->platform->dev); -} - -static struct drm_gem_object *vgem_prime_import_sg_table(struct drm_device *dev, - struct dma_buf_attachment *attach, struct sg_table *sg) -{ - struct drm_vgem_gem_object *obj; - int npages; - - obj = __vgem_gem_create(dev, attach->dmabuf->size); - if (IS_ERR(obj)) - return ERR_CAST(obj); + obj->map_wc = true;

- npages = PAGE_ALIGN(attach->dmabuf->size) / PAGE_SIZE; - - obj->table = sg; - obj->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL); - if (!obj->pages) { - __vgem_gem_destroy(obj); - return ERR_PTR(-ENOMEM); - } - - obj->pages_pin_count++; /* perma-pinned */ - drm_prime_sg_to_page_array(obj->table, obj->pages, npages); return &obj->base; }

-static int vgem_prime_vmap(struct drm_gem_object *obj, struct dma_buf_map *map) -{ - struct drm_vgem_gem_object *bo = to_vgem_bo(obj); - long n_pages = obj->size >> PAGE_SHIFT; - struct page **pages; - void *vaddr; - - pages = vgem_pin_pages(bo); - if (IS_ERR(pages)) - return PTR_ERR(pages); - - vaddr = vmap(pages, n_pages, 0, pgprot_writecombine(PAGE_KERNEL)); - if (!vaddr) - return -ENOMEM; - dma_buf_map_set_vaddr(map, vaddr); - - return 0; -} - -static void vgem_prime_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map) -{ - struct drm_vgem_gem_object *bo = to_vgem_bo(obj); - - vunmap(map->vaddr); - vgem_unpin_pages(bo); -} - -static int vgem_prime_mmap(struct drm_gem_object *obj, - struct vm_area_struct *vma) -{ - int ret; - - if (obj->size < vma->vm_end - vma->vm_start) - return -EINVAL; - - if (!obj->filp) - return -ENODEV; - - ret = call_mmap(obj->filp, vma); - if (ret) - return ret; - - vma_set_file(vma, obj->filp); - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP; - vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags)); - - return 0; -} - -static const struct drm_gem_object_funcs vgem_gem_object_funcs = { - .free = vgem_gem_free_object, - .pin = vgem_prime_pin, - .unpin = vgem_prime_unpin, - .get_sg_table = vgem_prime_get_sg_table, - .vmap = vgem_prime_vmap, - .vunmap = vgem_prime_vunmap, - .vm_ops = &vgem_gem_vm_ops, -}; - static const struct drm_driver vgem_driver = { .driver_features = DRIVER_GEM | DRIVER_RENDER, .open = vgem_open, @@ -427,13 +116,8 @@ static const struct drm_driver vgem_driver = { .num_ioctls = ARRAY_SIZE(vgem_ioctls), .fops = &vgem_driver_fops,

- .dumb_create = vgem_gem_dumb_create, - - .prime_handle_to_fd = drm_gem_prime_handle_to_fd, - .prime_fd_to_handle = drm_gem_prime_fd_to_handle, - .gem_prime_import = vgem_prime_import, - .gem_prime_import_sg_table = vgem_prime_import_sg_table, - .gem_prime_mmap = vgem_prime_mmap, + DRM_GEM_SHMEM_DRIVER_OPS, + .gem_create_object = vgem_gem_create_object,

.name = DRIVER_NAME, .desc = DRIVER_DESC,

On Thu, Jul 22, 2021 at 08:50:48PM +0200, Thomas Zimmermann wrote:

Hi

Am 13.07.21 um 22:51 schrieb Daniel Vetter:

...

Aside from deleting lots of code the real motivation here is to switch the mmap over to VM_PFNMAP, to be more consistent with what real gpu drivers do. They're all VM_PFNMP, which means get_user_pages doesn't work, and even if you try and there's a struct page behind that, touching it and mucking around with its refcount can upset drivers real bad.

v2: Review from Thomas:

• sort #include
• drop more dead code that I didn't spot somehow

v3: select DRM_GEM_SHMEM_HELPER to make it build (intel-gfx-ci)

v4: I got tricked by 0cf2ef46c6c0 ("drm/shmem-helper: Use cached mappings by default"), and we need WC in vgem because vgem doesn't have explicit begin/end cpu access ioctls.

Also add a comment why exactly vgem has to use wc.

v5: Don't set obj->base.funcs, it will default to drm_gem_shmem_funcs (Thomas)

v6: vgem also needs an MMU for remapping

Cc: Thomas Zimmermann tzimmermann@suse.de Acked-by: Thomas Zimmermann tzimmermann@suse.de Cc: John Stultz john.stultz@linaro.org Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Melissa Wen melissa.srw@gmail.com Cc: Chris Wilson chris@chris-wilson.co.uk

---

drivers/gpu/drm/Kconfig | 5 +- drivers/gpu/drm/vgem/vgem_drv.c | 315 ++------------------------------ 2 files changed, 15 insertions(+), 305 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 314eefa39892..28f7d2006e8b 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -272,7 +272,8 @@ source "drivers/gpu/drm/kmb/Kconfig" config DRM_VGEM tristate "Virtual GEM provider"

• depends on DRM

• depends on DRM && MMU
• select DRM_GEM_SHMEM_HELPER help Choose this option to get a virtual graphics memory manager, as used by Mesa's software renderer for enhanced performance.

@@ -280,7 +281,7 @@ config DRM_VGEM config DRM_VKMS tristate "Virtual KMS (EXPERIMENTAL)"

• depends on DRM

• depends on DRM && MMU select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER select CRC32

diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c index bf38a7e319d1..ba410ba6b7f7 100644 --- a/drivers/gpu/drm/vgem/vgem_drv.c +++ b/drivers/gpu/drm/vgem/vgem_drv.c @@ -38,6 +38,7 @@ #include <drm/drm_drv.h> #include <drm/drm_file.h> +#include <drm/drm_gem_shmem_helper.h> #include <drm/drm_ioctl.h> #include <drm/drm_managed.h> #include <drm/drm_prime.h> @@ -50,87 +51,11 @@ #define DRIVER_MAJOR 1 #define DRIVER_MINOR 0 -static const struct drm_gem_object_funcs vgem_gem_object_funcs;

• static struct vgem_device { struct drm_device drm; struct platform_device *platform; } *vgem_device;

-static void vgem_gem_free_object(struct drm_gem_object *obj) -{

• struct drm_vgem_gem_object *vgem_obj = to_vgem_bo(obj);
• kvfree(vgem_obj->pages);
• mutex_destroy(&vgem_obj->pages_lock);
• if (obj->import_attach)

• drm_prime_gem_destroy(obj, vgem_obj->table);
  

• drm_gem_object_release(obj);
• kfree(vgem_obj);

-}

-static vm_fault_t vgem_gem_fault(struct vm_fault *vmf) -{

• struct vm_area_struct *vma = vmf->vma;
• struct drm_vgem_gem_object *obj = vma->vm_private_data;
• /* We don't use vmf->pgoff since that has the fake offset */
• unsigned long vaddr = vmf->address;
• vm_fault_t ret = VM_FAULT_SIGBUS;
• loff_t num_pages;
• pgoff_t page_offset;
• page_offset = (vaddr - vma->vm_start) >> PAGE_SHIFT;
• num_pages = DIV_ROUND_UP(obj->base.size, PAGE_SIZE);
• if (page_offset >= num_pages)

• return VM_FAULT_SIGBUS;
  

• mutex_lock(&obj->pages_lock);
• if (obj->pages) {

• get_page(obj->pages[page_offset]);
  

• vmf->page = obj->pages[page_offset];
  

• ret = 0;
  

• }
• mutex_unlock(&obj->pages_lock);
• if (ret) {

• struct page *page;
  

• page = shmem_read_mapping_page(
  

• 			file_inode(obj->base.filp)->i_mapping,
  

• 			page_offset);
  

• if (!IS_ERR(page)) {
  

• 	vmf->page = page;
  

• 	ret = 0;
  

• } else switch (PTR_ERR(page)) {
  

• 	case -ENOSPC:
  

• 	case -ENOMEM:
  

• 		ret = VM_FAULT_OOM;
  

• 		break;
  

• 	case -EBUSY:
  

• 		ret = VM_FAULT_RETRY;
  

• 		break;
  

• 	case -EFAULT:
  

• 	case -EINVAL:
  

• 		ret = VM_FAULT_SIGBUS;
  

• 		break;
  

• 	default:
  

• 		WARN_ON(PTR_ERR(page));
  

• 		ret = VM_FAULT_SIGBUS;
  

• 		break;
  

• }
  

• }
• return ret;

-}

-static const struct vm_operations_struct vgem_gem_vm_ops = {

• .fault = vgem_gem_fault,
• .open = drm_gem_vm_open,
• .close = drm_gem_vm_close,

-};

• static int vgem_open(struct drm_device *dev, struct drm_file *file) { struct vgem_file *vfile;

@@ -159,81 +84,6 @@ static void vgem_postclose(struct drm_device *dev, struct drm_file *file) kfree(vfile); } -static struct drm_vgem_gem_object *__vgem_gem_create(struct drm_device *dev,

• 				unsigned long size)
  

-{

• struct drm_vgem_gem_object *obj;
• int ret;
• obj = kzalloc(sizeof(*obj), GFP_KERNEL);
• if (!obj)

• return ERR_PTR(-ENOMEM);
  

• obj->base.funcs = &vgem_gem_object_funcs;
• ret = drm_gem_object_init(dev, &obj->base, roundup(size, PAGE_SIZE));
• if (ret) {

• kfree(obj);
  

• return ERR_PTR(ret);
  

• }
• mutex_init(&obj->pages_lock);
• return obj;

-}

-static void __vgem_gem_destroy(struct drm_vgem_gem_object *obj) -{

• drm_gem_object_release(&obj->base);
• kfree(obj);

-}

-static struct drm_gem_object *vgem_gem_create(struct drm_device *dev,

• 			      struct drm_file *file,
  

• 			      unsigned int *handle,
  

• 			      unsigned long size)
  

-{

• struct drm_vgem_gem_object *obj;
• int ret;
• obj = __vgem_gem_create(dev, size);
• if (IS_ERR(obj))

• return ERR_CAST(obj);
  

• ret = drm_gem_handle_create(file, &obj->base, handle);
• if (ret) {

• drm_gem_object_put(&obj->base);
  

• return ERR_PTR(ret);
  

• }
• return &obj->base;

-}

-static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev,

• 		struct drm_mode_create_dumb *args)
  

-{

• struct drm_gem_object *gem_object;
• u64 pitch, size;
• pitch = args->width * DIV_ROUND_UP(args->bpp, 8);
• size = args->height * pitch;
• if (size == 0)

• return -EINVAL;
  

• gem_object = vgem_gem_create(dev, file, &args->handle, size);
• if (IS_ERR(gem_object))

• return PTR_ERR(gem_object);
  

• args->size = gem_object->size;
• args->pitch = pitch;
• drm_gem_object_put(gem_object);
• DRM_DEBUG("Created object of size %llu\n", args->size);
• return 0;

-}

• static struct drm_ioctl_desc vgem_ioctls[] = { DRM_IOCTL_DEF_DRV(VGEM_FENCE_ATTACH, vgem_fence_attach_ioctl, DRM_RENDER_ALLOW), DRM_IOCTL_DEF_DRV(VGEM_FENCE_SIGNAL, vgem_fence_signal_ioctl, DRM_RENDER_ALLOW),

@@ -266,159 +116,23 @@ static const struct file_operations vgem_driver_fops = { .release = drm_release, }; -static struct page **vgem_pin_pages(struct drm_vgem_gem_object *bo) -{

• mutex_lock(&bo->pages_lock);
• if (bo->pages_pin_count++ == 0) {

• struct page **pages;
  

• pages = drm_gem_get_pages(&bo->base);
  

• if (IS_ERR(pages)) {
  

• 	bo->pages_pin_count--;
  

• 	mutex_unlock(&bo->pages_lock);
  

• 	return pages;
  

• }
  

• bo->pages = pages;
  

• }
• mutex_unlock(&bo->pages_lock);
• return bo->pages;

-}

-static void vgem_unpin_pages(struct drm_vgem_gem_object *bo) +static struct drm_gem_object *vgem_gem_create_object(struct drm_device *dev, size_t size) {

• mutex_lock(&bo->pages_lock);
• if (--bo->pages_pin_count == 0) {

• drm_gem_put_pages(&bo->base, bo->pages, true, true);
  

• bo->pages = NULL;
  

• }
• mutex_unlock(&bo->pages_lock);

-}

• struct drm_gem_shmem_object *obj;

-static int vgem_prime_pin(struct drm_gem_object *obj) -{

• struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
• long n_pages = obj->size >> PAGE_SHIFT;
• struct page **pages;
• pages = vgem_pin_pages(bo);
• if (IS_ERR(pages))

• return PTR_ERR(pages);
  

• obj = kzalloc(sizeof(*obj), GFP_KERNEL);
• if (!obj)

• return NULL;
  

• /* Flush the object from the CPU cache so that importers can rely

• * on coherent indirect access via the exported dma-address.
  

• /*

• * vgem doesn't have any begin/end cpu access ioctls, therefore must use
  

• * coherent memory or dma-buf sharing just wont work.
  

  */

• drm_clflush_pages(pages, n_pages);

Instead of shoehorning GEM SHMEM to get caching right (patch 2) have you considered to set your own GEM funcs object for vgem. All function pointers would point to SHMEM functions, except for pin, which would be drm_gem_shmem_pin() + drm_clflush_pages(). If this works, I think it would be much preferable to the current patch 2. You can override the default GEM functions from within vgem_gem_create_object().

The thing is: shmem helpers currently get the caching wrong for wc. vgem is just the messenger.

Also, get_pages + drm_clflush is not actually guaranteed to be enough across platforms. It is enough on intel x86 cpus (and I think all modern amd x86 cpus, but not some earlier ones from way back), but not in general across the board. -Daniel

Best regards Thomas

...

• return 0;

-}

-static void vgem_prime_unpin(struct drm_gem_object *obj) -{

• struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
• vgem_unpin_pages(bo);

-}

-static struct sg_table *vgem_prime_get_sg_table(struct drm_gem_object *obj) -{

• struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
• return drm_prime_pages_to_sg(obj->dev, bo->pages, bo->base.size >> PAGE_SHIFT);

-}

-static struct drm_gem_object* vgem_prime_import(struct drm_device *dev,

• 				struct dma_buf *dma_buf)
  

-{

• struct vgem_device *vgem = container_of(dev, typeof(*vgem), drm);
• return drm_gem_prime_import_dev(dev, dma_buf, &vgem->platform->dev);

-}

-static struct drm_gem_object *vgem_prime_import_sg_table(struct drm_device *dev,

• 	struct dma_buf_attachment *attach, struct sg_table *sg)
  

-{

• struct drm_vgem_gem_object *obj;
• int npages;
• obj = __vgem_gem_create(dev, attach->dmabuf->size);
• if (IS_ERR(obj))

• return ERR_CAST(obj);
  

• npages = PAGE_ALIGN(attach->dmabuf->size) / PAGE_SIZE;
• obj->table = sg;
• obj->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
• if (!obj->pages) {

• __vgem_gem_destroy(obj);
  

• return ERR_PTR(-ENOMEM);
  

• }

• obj->map_wc = true;

• obj->pages_pin_count++; /* perma-pinned */
• drm_prime_sg_to_page_array(obj->table, obj->pages, npages); return &obj->base; }

-static int vgem_prime_vmap(struct drm_gem_object *obj, struct dma_buf_map *map) -{

• struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
• long n_pages = obj->size >> PAGE_SHIFT;
• struct page **pages;
• void *vaddr;
• pages = vgem_pin_pages(bo);
• if (IS_ERR(pages))

• return PTR_ERR(pages);
  

• vaddr = vmap(pages, n_pages, 0, pgprot_writecombine(PAGE_KERNEL));
• if (!vaddr)

• return -ENOMEM;
  

• dma_buf_map_set_vaddr(map, vaddr);
• return 0;

-}

-static void vgem_prime_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map) -{

• struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
• vunmap(map->vaddr);
• vgem_unpin_pages(bo);

-}

-static int vgem_prime_mmap(struct drm_gem_object *obj,

• 	   struct vm_area_struct *vma)
  

-{

• int ret;
• if (obj->size < vma->vm_end - vma->vm_start)

• return -EINVAL;
  

• if (!obj->filp)

• return -ENODEV;
  

• ret = call_mmap(obj->filp, vma);
• if (ret)

• return ret;
  

• vma_set_file(vma, obj->filp);
• vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
• vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
• return 0;

-}

-static const struct drm_gem_object_funcs vgem_gem_object_funcs = {

• .free = vgem_gem_free_object,
• .pin = vgem_prime_pin,
• .unpin = vgem_prime_unpin,
• .get_sg_table = vgem_prime_get_sg_table,
• .vmap = vgem_prime_vmap,
• .vunmap = vgem_prime_vunmap,
• .vm_ops = &vgem_gem_vm_ops,

-};

• static const struct drm_driver vgem_driver = { .driver_features = DRIVER_GEM | DRIVER_RENDER, .open = vgem_open,

@@ -427,13 +141,8 @@ static const struct drm_driver vgem_driver = { .num_ioctls = ARRAY_SIZE(vgem_ioctls), .fops = &vgem_driver_fops,

• .dumb_create = vgem_gem_dumb_create,
• .prime_handle_to_fd = drm_gem_prime_handle_to_fd,
• .prime_fd_to_handle = drm_gem_prime_fd_to_handle,
• .gem_prime_import = vgem_prime_import,
• .gem_prime_import_sg_table = vgem_prime_import_sg_table,
• .gem_prime_mmap = vgem_prime_mmap,

• DRM_GEM_SHMEM_DRIVER_OPS,
• .gem_create_object = vgem_gem_create_object, .name = DRIVER_NAME, .desc = DRIVER_DESC,

-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer