Am 21.08.2019 20:28 schrieb "Thomas Hellström (VMware)" thomas_os@shipmail.org: On 8/21/19 8:11 PM, Daniel Vetter wrote:
On Wed, Aug 21, 2019 at 7:06 PM Thomas Hellström (VMware) thomas_os@shipmail.org wrote:
On 8/21/19 6:34 PM, Daniel Vetter wrote:
On Wed, Aug 21, 2019 at 05:54:27PM +0200, Thomas Hellström (VMware) wrote:
On 8/20/19 4:53 PM, Daniel Vetter wrote:
Full audit of everyone:
i915, radeon, amdgpu should be clean per their maintainers.
vram helpers should be fine, they don't do command submission, so really no business holding struct_mutex while doing copy_*_user. But I haven't checked them all.
panfrost seems to dma_resv_lock only in panfrost_job_push, which looks clean.
v3d holds dma_resv locks in the tail of its v3d_submit_cl_ioctl(), copying from/to userspace happens all in v3d_lookup_bos which is outside of the critical section.
vmwgfx has a bunch of ioctls that do their own copy_*_user:
- vmw_execbuf_process: First this does some copies in vmw_execbuf_cmdbuf() and also in the vmw_execbuf_process() itself. Then comes the usual ttm reserve/validate sequence, then actual submission/fencing, then unreserving, and finally some more copy_to_user in vmw_execbuf_copy_fence_user. Glossing over tons of details, but looks all safe.
- vmw_fence_event_ioctl: No ttm_reserve/dma_resv_lock anywhere to be seen, seems to only create a fence and copy it out.
- a pile of smaller ioctl in vmwgfx_ioctl.c, no reservations to be found there.
Summary: vmwgfx seems to be fine too.
virtio: There's virtio_gpu_execbuffer_ioctl, which does all the copying from userspace before even looking up objects through their handles, so safe. Plus the getparam/getcaps ioctl, also both safe.
qxl only has qxl_execbuffer_ioctl, which calls into qxl_process_single_command. There's a lovely comment before the __copy_from_user_inatomic that the slowpath should be copied from i915, but I guess that never happened. Try not to be unlucky and get your CS data evicted between when it's written and the kernel tries to read it. The only other copy_from_user is for relocs, but those are done before qxl_release_reserve_list(), which seems to be the only thing reserving buffers (in the ttm/dma_resv sense) in that code. So looks safe.
A debugfs file in nouveau_debugfs_pstate_set() and the usif ioctl in usif_ioctl() look safe. nouveau_gem_ioctl_pushbuf() otoh breaks this everywhere and needs to be fixed up.
Cc: Alex Deucher alexander.deucher@amd.com Cc: Christian König christian.koenig@amd.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Thomas Zimmermann tzimmermann@suse.de Cc: Rob Herring robh@kernel.org Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Eric Anholt eric@anholt.net Cc: Dave Airlie airlied@redhat.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Ben Skeggs bskeggs@redhat.com Cc: "VMware Graphics" linux-graphics-maintainer@vmware.com Cc: Thomas Hellstrom thellstrom@vmware.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com
drivers/dma-buf/dma-resv.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 42a8f3f11681..3edca10d3faf 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -34,6 +34,7 @@ #include <linux/dma-resv.h> #include <linux/export.h> +#include <linux/sched/mm.h> /** * DOC: Reservation Object Overview @@ -107,6 +108,17 @@ void dma_resv_init(struct dma_resv *obj) &reservation_seqcount_class); RCU_INIT_POINTER(obj->fence, NULL); RCU_INIT_POINTER(obj->fence_excl, NULL);
- if (IS_ENABLED(CONFIG_LOCKDEP)) {
if (current->mm)down_read(¤t->mm->mmap_sem);ww_mutex_lock(&obj->lock, NULL);fs_reclaim_acquire(GFP_KERNEL);fs_reclaim_release(GFP_KERNEL);ww_mutex_unlock(&obj->lock);if (current->mm)up_read(¤t->mm->mmap_sem);- } } EXPORT_SYMBOL(dma_resv_init);
I assume if this would have been easily done and maintainable using only lockdep annotation instead of actually acquiring the locks, that would have been done?
There's might_lock(), plus a pile of macros, but they don't map obviuosly, so pretty good chances I accidentally end up with the wrong type of annotation. Easier to just take the locks quickly, and stuff that all into a lockdep-only section to avoid overhead.
Otherwise LGTM.
Reviewed-by: Thomas Hellström thellstrom@vmware.com
Will test this and let you know if it trips on vmwgfx, but it really shouldn't.
Thanks, Daniel
One thing that strikes me is that this puts restrictions on where you can actually initialize a dma_resv, even if locking orders are otherwise obeyed. But that might not be a big problem.
Hm yeah ... the trouble is a need a non-kthread thread so that I have a current->mm. Otherwise I'd have put it into some init section with a temp dma_buf. And I kinda don't want to create a fake ->mm just for lockdep priming. I don't expect this to be a real problem in practice, since before you've called dma_resv_init the reservation lock doesn't exist, so you can't hold it. And you've probably just allocated it, so fs_reclaim is going to be fine. And if you allocate dma_resv objects from your fault handlers I have questions anyway :-)
Coming to think of it, I think vmwgfx sometimes create bos with other bo's reservation lock held. I guess that would trip both the mmap_sem check the ww_mutex check?
Dito inside TTM for ghost objects.
We even used to have an dma_resv_init() in an atomic section, but that should be gone by now.
Anyway, probably have to take my review back since this will certainly go up in flames.
Need a better place for this, Christian.
/Thomas
/Thomas
So I think this should be safe. -Daniel
dri-devel@lists.freedesktop.org
-
Koenig, Christian