[PATCH 6/9] drm/i915/shmem: ensure flush during swap-in on non-LLC

[Matthew Auld]

On non-LLC platforms, force the flush-on-acquire if this is ever
swapped-in. Our async flush path is not trust worthy enough yet(and
happens in the wrong order), and with some tricks it's conceivable for
userspace to change the cache-level to I915_CACHE_NONE after the pages
are swapped-in, and since execbuf binds the object before doing the
async flush, there is a potential race window.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index cf11aa7e08a0..d77da59fae04 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -286,6 +286,8 @@ __i915_gem_object_release_shmem(struct drm_i915_gem_object *obj,
 				struct sg_table *pages,
 				bool needs_clflush)
 {
+	struct drm_i915_private *i915 = to_i915(obj->base.dev);
+
 	GEM_BUG_ON(obj->mm.madv == __I915_MADV_PURGED);
 
 	if (obj->mm.madv == I915_MADV_DONTNEED)
@@ -297,6 +299,16 @@ __i915_gem_object_release_shmem(struct drm_i915_gem_object *obj,
 		drm_clflush_sg(pages);
 
 	__start_cpu_write(obj);
+	/*
+	 * On non-LLC platforms, force the flush-on-acquire if this is ever
+	 * swapped-in. Our async flush path is not trust worthy enough yet(and
+	 * happens in the wrong order), and with some tricks it's conceivable
+	 * for userspace to change the cache-level to I915_CACHE_NONE after the
+	 * pages are swapped-in, and since execbuf binds the object before doing
+	 * the async flush, we have a race window.
+	 */
+	if (!HAS_LLC(i915))
+		obj->cache_dirty = true;
 }
 
 void i915_gem_object_put_pages_shmem(struct drm_i915_gem_object *obj, struct sg_table *pages)
-- 
2.26.3