Re: [PATCH v2 2/2] drm/i915: check memory is mappable in read_from_page

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Reviewed-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>

On 9/30/2022 3:47 PM, Matthew Auld wrote:
On small-bar systems we could be given something non-mappable here,
which leads to nasty oops. Make this nicer by checking if the resource
is mappable or not, and return an error otherwise.

v2: drop GEM_BUG_ON(flags & I915_BO_ALLOC_GPU_ONLY)

Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Jianshui Yu <jianshui.yu@xxxxxxxxx>
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: Nirmoy Das <nirmoy.das@xxxxxxxxx>
---
  drivers/gpu/drm/i915/gem/i915_gem_object.c | 12 +++++++++++-
  1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 369006c5317f..62495d5d0038 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -444,6 +444,16 @@ i915_gem_object_read_from_page_iomap(struct drm_i915_gem_object *obj, u64 offset
  	io_mapping_unmap(src_map);
  }
+static bool object_has_mappable_iomem(struct drm_i915_gem_object *obj)
+{
+	GEM_BUG_ON(!i915_gem_object_has_iomem(obj));
+
+	if (IS_DGFX(to_i915(obj->base.dev)))
+		return i915_ttm_resource_mappable(i915_gem_to_ttm(obj)->resource);
+
+	return true;
+}
+
  /**
   * i915_gem_object_read_from_page - read data from the page of a GEM object
   * @obj: GEM object to read from
@@ -466,7 +476,7 @@ int i915_gem_object_read_from_page(struct drm_i915_gem_object *obj, u64 offset,
if (i915_gem_object_has_struct_page(obj))
  		i915_gem_object_read_from_page_kmap(obj, offset, dst, size);
-	else if (i915_gem_object_has_iomem(obj))
+	else if (i915_gem_object_has_iomem(obj) && object_has_mappable_iomem(obj))
  		i915_gem_object_read_from_page_iomap(obj, offset, dst, size);
  	else
  		return -ENODEV;



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