On Wed, Jan 27, 2021 at 09:29:41AM -0500, Andrey Grodzovsky wrote:
Hey Daniel, just a ping.
Was on vacations last week.
Andrey
On 1/25/21 10:28 AM, Andrey Grodzovsky wrote:
On 1/19/21 8:56 AM, Daniel Vetter wrote:
On Mon, Jan 18, 2021 at 04:01:10PM -0500, Andrey Grodzovsky wrote:
On device removal reroute all CPU mappings to dummy page.
v3: Remove loop to find DRM file and instead access it by vma->vm_file->private_data. Move dummy page installation into a separate function.
v4: Map the entire BOs VA space into on demand allocated dummy page on the first fault for that BO.
Signed-off-by: Andrey Grodzovsky andrey.grodzovsky@amd.com
drivers/gpu/drm/ttm/ttm_bo_vm.c | 82 ++++++++++++++++++++++++++++++++++++++++- include/drm/ttm/ttm_bo_api.h | 2 + 2 files changed, 83 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c index 6dc96cf..ed89da3 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c @@ -34,6 +34,8 @@ #include <drm/ttm/ttm_bo_driver.h> #include <drm/ttm/ttm_placement.h> #include <drm/drm_vma_manager.h> +#include <drm/drm_drv.h> +#include <drm/drm_managed.h> #include <linux/mm.h> #include <linux/pfn_t.h> #include <linux/rbtree.h> @@ -380,25 +382,103 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf, } EXPORT_SYMBOL(ttm_bo_vm_fault_reserved); +static void ttm_bo_release_dummy_page(struct drm_device *dev, void *res) +{ + struct page *dummy_page = (struct page *)res;
+ __free_page(dummy_page); +}
+vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot) +{ + struct vm_area_struct *vma = vmf->vma; + struct ttm_buffer_object *bo = vma->vm_private_data; + struct ttm_bo_device *bdev = bo->bdev; + struct drm_device *ddev = bo->base.dev; + vm_fault_t ret = VM_FAULT_NOPAGE; + unsigned long address = vma->vm_start; + unsigned long num_prefault = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT; + unsigned long pfn; + struct page *page; + int i;
+ /* + * Wait for buffer data in transit, due to a pipelined + * move. + */ + ret = ttm_bo_vm_fault_idle(bo, vmf); + if (unlikely(ret != 0)) + return ret;
+ /* Allocate new dummy page to map all the VA range in this VMA to it*/ + page = alloc_page(GFP_KERNEL | __GFP_ZERO); + if (!page) + return VM_FAULT_OOM;
+ pfn = page_to_pfn(page);
+ /* + * Prefault the entire VMA range right away to avoid further faults + */ + for (i = 0; i < num_prefault; ++i) {
+ if (unlikely(address >= vma->vm_end)) + break;
+ if (vma->vm_flags & VM_MIXEDMAP) + ret = vmf_insert_mixed_prot(vma, address, + __pfn_to_pfn_t(pfn, PFN_DEV), + prot); + else + ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
+ /* Never error on prefaulted PTEs */ + if (unlikely((ret & VM_FAULT_ERROR))) { + if (i == 0) + return VM_FAULT_NOPAGE; + else + break; + }
+ address += PAGE_SIZE; + }
+ /* Set the page to be freed using drmm release action */ + if (drmm_add_action_or_reset(ddev, ttm_bo_release_dummy_page, page)) + return VM_FAULT_OOM;
+ return ret; +} +EXPORT_SYMBOL(ttm_bo_vm_dummy_page);
I think we can lift this entire thing (once the ttm_bo_vm_fault_idle is gone) to the drm level, since nothing ttm specific in here. Probably stuff it into drm_gem.c (but really it's not even gem specific, it's fully generic "replace this vma with dummy pages pls" function.
Once I started with this I noticed that drmm_add_action_or_reset depends on struct drm_device *ddev = bo->base.dev and bo is the private data we embed at the TTM level when setting up the mapping and so this forces to move drmm_add_action_or_reset out of this function to every client who uses this function, and then you separate the logic of page allocation from it's release. So I suggest we keep it as is.
Uh disappointing. Thing is, ttm essentially means drm devices with gem, except for vmwgfx, which is a drm_device without gem. And I think one of the remaining ttm refactors in this area is to move ttm_device over into drm_device someone, and then we'd have bo->base.dev always set to something that drmm_add_action_or_reset can use.
I guess hand-rolling for now and jotting this down as a TODO item is fine too, but would be good to get this addressed since that's another reason here to do this. Maybe sync with Christian how to best do this. -Daniel
Andrey
Aside from this nit I think the overall approach you have here is starting to look good. Lots of work&polish, but imo we're getting there and can start landing stuff soon. -Daniel
vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; pgprot_t prot; struct ttm_buffer_object *bo = vma->vm_private_data; + struct drm_device *ddev = bo->base.dev; vm_fault_t ret; + int idx; ret = ttm_bo_vm_reserve(bo, vmf); if (ret) return ret; prot = vma->vm_page_prot; - ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1); + if (drm_dev_enter(ddev, &idx)) { + ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1); + drm_dev_exit(idx); + } else { + ret = ttm_bo_vm_dummy_page(vmf, prot); + } if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) return ret; dma_resv_unlock(bo->base.resv); return ret;
+ return ret; } EXPORT_SYMBOL(ttm_bo_vm_fault); diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h index e17be32..12fb240 100644 --- a/include/drm/ttm/ttm_bo_api.h +++ b/include/drm/ttm/ttm_bo_api.h @@ -643,4 +643,6 @@ void ttm_bo_vm_close(struct vm_area_struct *vma); int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr, void *buf, int len, int write); +vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot);
#endif
2.7.4