drm/amdgpu: zero-initialize GART table on allocation

commit e6c2e6c upstream.

GART TLB is flushed after unmapping but not after mapping. Since
amdgpu_bo_create_kernel() does not zero-initialize the buffer, when a
single PTE is written the TLB may speculatively load other uninitialized
entries from the same cacheline. Those garbage entries can appear valid,
and a subsequent write to another PTE in the same cacheline may cause the
GPU to use a stale garbage PTE from the TLB.

Fix this by calling memset_io() to zero-initialize the GART table with
gart_pte_flags immediately after allocation.

Using AMDGPU_GEM_CREATE_VRAM_CLEARED, SDMA-based clear will not work
since SDMA needs GART to be initialized to work.

Suggested-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit d9af826)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: amd-yangp

drivers/gpu/drm/amd/amdgpu/amdgpu_gart.c

@@ -252,12 +252,19 @@ void amdgpu_gart_table_ram_free(struct amdgpu_device *adev)
  */
 int amdgpu_gart_table_vram_alloc(struct amdgpu_device *adev)
 {
+	int r;
+
 	if (adev->gart.bo != NULL)
 		return 0;
 
-	return amdgpu_bo_create_kernel(adev,  adev->gart.table_size, PAGE_SIZE,
-				       AMDGPU_GEM_DOMAIN_VRAM, &adev->gart.bo,
-				       NULL, (void *)&adev->gart.ptr);
+	r = amdgpu_bo_create_kernel(adev,  adev->gart.table_size, PAGE_SIZE,
+				    AMDGPU_GEM_DOMAIN_VRAM, &adev->gart.bo,
+				    NULL, (void *)&adev->gart.ptr);
+	if (r)
+		return r;
+
+	memset_io(adev->gart.ptr, adev->gart.gart_pte_flags, adev->gart.table_size);
+	return 0;
 }
 
 /**