From: Zhao Liu <zhao1....@intel.com> The use of kmap_atomic() is being deprecated in favor of kmap_local_page()[1].
The main difference between atomic and local mappings is that local mappings doesn't disable page faults or preemption. There're 2 reasons why i915_gem_object_read_from_page_kmap() doesn't need to disable pagefaults and preemption for mapping: 1. The flush operation is safe for CPU hotplug when preemption is not disabled. In drm/i915/gem/i915_gem_object.c, the function i915_gem_object_read_from_page_kmap() calls drm_clflush_virt_range() to use CLFLUSHOPT or WBINVD to flush. Since CLFLUSHOPT is global on x86 and WBINVD is called on each cpu in drm_clflush_virt_range(), the flush operation is global and any issue with cpu's being added or removed can be handled safely. 2. Any context switch caused by preemption or sleep (pagefault may cause sleep) doesn't affect the validity of local mapping. Therefore, i915_gem_object_read_from_page_kmap() is a function where the use of kmap_local_page() in place of kmap_atomic() is correctly suited. Convert the calls of kmap_atomic() / kunmap_atomic() to kmap_local_page() / kunmap_local(). And remove the redundant variable that stores the address of the mapped page since kunmap_local() can accept any pointer within the page. [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.we...@intel.com Suggested-by: Dave Hansen <dave.han...@intel.com> Suggested-by: Ira Weiny <ira.we...@intel.com> Suggested-by: Fabio M. De Francesco <fmdefrance...@gmail.com> Signed-off-by: Zhao Liu <zhao1....@intel.com> --- Suggested by credits: Dave: Referred to his explanation about cache flush. Ira: Referred to his task document, review comments and explanation about cache flush. Fabio: Referred to his boiler plate commit message. --- drivers/gpu/drm/i915/gem/i915_gem_object.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c index 369006c5317f..a0072abed75e 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c @@ -413,17 +413,15 @@ void __i915_gem_object_invalidate_frontbuffer(struct drm_i915_gem_object *obj, static void i915_gem_object_read_from_page_kmap(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size) { - void *src_map; void *src_ptr; - src_map = kmap_atomic(i915_gem_object_get_page(obj, offset >> PAGE_SHIFT)); - - src_ptr = src_map + offset_in_page(offset); + src_ptr = kmap_local_page(i915_gem_object_get_page(obj, offset >> PAGE_SHIFT)) + + offset_in_page(offset); if (!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_READ)) drm_clflush_virt_range(src_ptr, size); memcpy(dst, src_ptr, size); - kunmap_atomic(src_map); + kunmap_local(src_ptr); } static void -- 2.34.1
