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drm/i915: Move the mb() following release-mmap into release-mmap 

As paranoia, we want to ensure that the CPU's PTEs have been revoked for
the object before we return from i915_gem_release_mmap(). This allows us
to rely on there being no outstanding memory accesses from userspace
and guarantees serialisation of the code against concurrent access just
by calling i915_gem_release_mmap().

v2: Reduce the mb() into a wmb() following the revoke.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: "Goel, Akash" <akash.goel@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1460565315-7748-13-git-send-email-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2016-04-13 17:35:12 +01:00
parent a687a43a48
commit 349f2ccff9
1 changed files with 16 additions and 3 deletions
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19
drivers/gpu/drm/i915/i915_gem.c
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@ -1936,11 +1936,27 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
void
i915_gem_release_mmap(struct drm_i915_gem_object *obj)
{
/* Serialisation between user GTT access and our code depends upon
* revoking the CPU's PTE whilst the mutex is held. The next user
* pagefault then has to wait until we release the mutex.
*/
lockdep_assert_held(&obj->base.dev->struct_mutex);
if (!obj->fault_mappable)
return;
drm_vma_node_unmap(&obj->base.vma_node,
obj->base.dev->anon_inode->i_mapping);
/* Ensure that the CPU's PTE are revoked and there are not outstanding
* memory transactions from userspace before we return. The TLB
* flushing implied above by changing the PTE above *should* be
* sufficient, an extra barrier here just provides us with a bit
* of paranoid documentation about our requirement to serialise
* memory writes before touching registers / GSM.
*/
wmb();
obj->fault_mappable = false;
}
@ -3324,9 +3340,6 @@ static void i915_gem_object_finish_gtt(struct drm_i915_gem_object *obj)
if ((obj->base.read_domains & I915_GEM_DOMAIN_GTT) == 0)
return;
/* Wait for any direct GTT access to complete */
mb();
old_read_domains = obj->base.read_domains;
old_write_domain = obj->base.write_domain;