drm/i915/userptr: add paranoid flush-on-acquire

Even though userptr objects are always coherent with the GPU, with no
way for userspace to change this with the set_caching ioctl, even on
non-LLC platforms, there is still the 'Bypass LCC' mocs setting, which
might permit reading the contents of main memory directly.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211018174508.2137279-5-matthew.auld@intel.com

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 887aca9..3173c9f 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -165,8 +165,11 @@ alloc_table:
                goto err;
        }
 
-       sg_page_sizes = i915_sg_dma_sizes(st->sgl);
+       WARN_ON_ONCE(!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_WRITE));
+       if (i915_gem_object_can_bypass_llc(obj))
+               obj->cache_dirty = true;
 
+       sg_page_sizes = i915_sg_dma_sizes(st->sgl);
        __i915_gem_object_set_pages(obj, st, sg_page_sizes);
 
        return 0;