From: Zhao Liu
The use of kmap_atomic() is being deprecated in favor of
kmap_local_page()[1], and this patch converts the call from
kmap_atomic() to kmap_local_page().
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/selftests/huge_pages.c, function __cpu_check_shmem()
mainly uses mapping to flush cache and check the value. There're
2 reasons why __cpu_check_shmem() doesn't need to disable pagefaults
and preemption for mapping:
1. The flush operation is safe. Function __cpu_check_shmem() 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.
2. Any context switch caused by preemption or page faults (page fault
may cause sleep) doesn't affect the validity of local mapping.
Therefore, __cpu_check_shmem() 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().
[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.we...@intel.com
v2:
* Dropped hot plug related description since it has nothing to do with
kmap_local_page().
* No code change since v1, and added description of the motivation of
using kmap_local_page().
Suggested-by: Dave Hansen
Suggested-by: Ira Weiny
Suggested-by: Fabio M. De Francesco
Signed-off-by: Zhao Liu
---
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 and his description
about why kmap_local_page() should be preferred.
---
drivers/gpu/drm/i915/gem/selftests/huge_pages.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
index defece0bcb81..3f9ea48a48d0 100644
--- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
+++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
@@ -1026,7 +1026,7 @@ __cpu_check_shmem(struct drm_i915_gem_object *obj, u32
dword, u32 val)
goto err_unlock;
for (n = 0; n < obj->base.size >> PAGE_SHIFT; ++n) {
- u32 *ptr = kmap_atomic(i915_gem_object_get_page(obj, n));
+ u32 *ptr = kmap_local_page(i915_gem_object_get_page(obj, n));
if (needs_flush & CLFLUSH_BEFORE)
drm_clflush_virt_range(ptr, PAGE_SIZE);
@@ -1034,12 +1034,12 @@ __cpu_check_shmem(struct drm_i915_gem_object *obj, u32
dword, u32 val)
if (ptr[dword] != val) {
pr_err("n=%lu ptr[%u]=%u, val=%u\n",
n, dword, ptr[dword], val);
- kunmap_atomic(ptr);
+ kunmap_local(ptr);
err = -EINVAL;
break;
}
- kunmap_atomic(ptr);
+ kunmap_local(ptr);
}
i915_gem_object_finish_access(obj);
--
2.34.1
