From 349f2ccff94e835210b253ec9bef1d97d6afb312 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Wed, 13 Apr 2016 17:35:12 +0100 Subject: [PATCH] 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Move the mb() following release-mmap into release-mmap As paranoia, we want to ensure that the CPU's PTEs have been revoked for the object before we return from i915_gem_release_mmap().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 Cc: Tvrtko Ursulin Cc: "Goel, Akash" Cc: Daniel Vetter Reviewed-by: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/1460565315-7748-13-git-send-email-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_gem.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 0c57b20532be..21fb41c93caa 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1936,11 +1936,27 @@ 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); + 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; -- 2.20.1