Re: [PATCH 5/9] drm/i915/userptr: add paranoid flush-on-acquire

[Thomas Hellström]

On 10/18/21 19:45, Matthew Auld wrote:

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.a...@intel.com>
Cc: Thomas Hellström <thomas.hellst...@linux.intel.com>
---
  drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: Thomas Hellström <thomas.hellst...@linux.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 887aca9e8dd2..3173c9f9a040 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -165,8 +165,11 @@ static int i915_gem_userptr_get_pages(struct 
drm_i915_gem_object *obj)
                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;