On Tue, Nov 24, 2015 at 02:36:43PM +0100, Daniel Vetter wrote:
> On Fri, Nov 20, 2015 at 10:31:38AM +0000, Chris Wilson wrote:
> > As paranoia, we want to ensure that the CPU's PTEs have been revoked for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 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@xxxxxxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> > Cc: "Goel, Akash" <akash.goel@xxxxxxxxx
> > ---
> > drivers/gpu/drm/i915/i915_gem.c | 13 ++++++++++---
> > 1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index df234d00b376..09c829f38786 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -1903,11 +1903,21 @@ out:
> > 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);
>
> lockdep_assert_held is a nop without lockdep, that's why I prefer
> WARN_ON(!mutex_is_locked). Either way:
I thought someone proposed adding i915_assert_held() or something
at one point? Or did I just imagine it?
>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
> > +
> > 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 before we return */
> > + wmb();
> > +
> > obj->fault_mappable = false;
> > }
> >
> > @@ -3212,9 +3222,6 @@ 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;
> >
> > --
> > 2.6.2
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Ville Syrjälä
Intel OTC
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