[patch] problems with "fix visible VRAM handling during faults"

[Jeremy Day <jsday@xxxxxxxxxxx>]

This is just to report that I've had usually well-behaved applications
sometimes having problems with memory access violations since kernel
version 6.9-rc5.  This past weekend I stumbled across a way to reliably
reproduce the problem in the form of a Skyrim save file which causes a
crash shortly after loading the game on affected kernels.

Things go back to running smoothly only if I revert one of the changes
in 5th April's "[PATCH] drm/amdgpu: fix visible VRAM handling during
faults" as follows.

Patch is against v6.9-rc7.  It restores the check for partially
visible-to-cpu memory in amdgpu_bo_fault_reserve_notify.  Things
seem stable again with this change.

--
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.c |  5 ++++-
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.h | 22 ++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
index f6d503432a9e..a6874aea7820 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
@@ -1396,7 +1396,10 @@ vm_fault_t amdgpu_bo_fault_reserve_notify(struct ttm_buffer_object *bo)
     /* Remember that this BO was accessed by the CPU */
     abo->flags |= AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
 
-    if (amdgpu_res_cpu_visible(adev, bo->resource))
+    if (bo->resource->mem_type != TTM_PL_VRAM)
+        return 0;
+
+    if (amdgpu_bo_in_cpu_visible_vram(abo))
         return 0;
 
     /* Can't move a pinned BO to visible VRAM */
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
index bc42ccbde659..0503af75dc26 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
@@ -250,6 +250,28 @@ static inline u64 amdgpu_bo_mmap_offset(struct amdgpu_bo *bo)
     return drm_vma_node_offset_addr(&bo->tbo.base.vma_node);
 }
 
+/**
+ * amdgpu_bo_in_cpu_visible_vram - check if BO is (partly) in visible VRAM
+ */
+static inline bool amdgpu_bo_in_cpu_visible_vram(struct amdgpu_bo *bo)
+{
+    struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
+    struct amdgpu_res_cursor cursor;
+
+    if (!bo->tbo.resource || bo->tbo.resource->mem_type != TTM_PL_VRAM)
+        return false;
+
+    amdgpu_res_first(bo->tbo.resource, 0, amdgpu_bo_size(bo), &cursor);
+    while (cursor.remaining) {
+        if (cursor.start < adev->gmc.visible_vram_size)
+            return true;
+
+        amdgpu_res_next(&cursor, cursor.size);
+    }
+
+    return false;
+}
+
 /**
  * amdgpu_bo_explicit_sync - return whether the bo is explicitly synced
  */