From: Zhao Liu <zhao1.liu@intel.com>
Date: Sun, 3 Dec 2023 13:29:41 +0000 (+0800)
Subject: drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=756eed0f2602f73df8d6c5bc8418ecd11cce9803;p=linux.git

drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c

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 (the preemption is
disabled for !PREEMPT_RT case, otherwise it only disables migration).

With kmap_local_page(), we can avoid the often unwanted side effect of
unnecessary page faults or preemption disables.

In drm/i915/gem/i915_gem_shmem.c, the function shmem_pwrite() need to
disable pagefault to eliminate the potential recursion fault[2]. But
here __copy_from_user_inatomic() doesn't need to disable preemption and
local mapping is valid for sched in/out.

So it can use kmap_local_page() / kunmap_local() with
pagefault_disable() / pagefault_enable() to replace atomic mapping.

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com
[2]: https://patchwork.freedesktop.org/patch/295840/

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231203132947.2328805-4-zhao1.liu@linux.intel.com
---

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index 73a4a4eb29e08..38b72d86560f0 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -485,11 +485,13 @@ shmem_pwrite(struct drm_i915_gem_object *obj,
 		if (err < 0)
 			return err;
 
-		vaddr = kmap_atomic(page);
+		vaddr = kmap_local_page(page);
+		pagefault_disable();
 		unwritten = __copy_from_user_inatomic(vaddr + pg,
 						      user_data,
 						      len);
-		kunmap_atomic(vaddr);
+		pagefault_enable();
+		kunmap_local(vaddr);
 
 		err = aops->write_end(obj->base.filp, mapping, offset, len,
 				      len - unwritten, page, data);