Re: [PATCH v2] drm/amdkfd: Use huge page size to check split svm range alignment

[Philip Yang]

On 2025-11-14 18:26, Felix Kuehling wrote:

On 2025-11-13 16:09, Xiaogang.Chen wrote:
From: Xiaogang Chen <xiaogang.c...@amd.com>

Fixes: 7ef6b2d4b7e5 (drm/amdkfd: remap unaligned svm ranges that have 
split)

When split svm ranges that have been mapped using huge page should 
use huge
page size(2MB) to check split range alignment, not 
prange->granularity that
means migration granularity.

Signed-off-by: Xiaogang Chen <xiaogang.c...@amd.com>
---
  drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 16 ++++++++++++----
  1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c 
b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index 521c14c7a789..c60d8134db45 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -1146,11 +1146,14 @@ svm_range_split_tail(struct svm_range 
*prange, uint64_t new_last,
  {
      struct svm_range *tail = NULL;
      int r = svm_range_split(prange, prange->start, new_last, &tail);
+    bool huge_page_mapping = IS_ALIGNED(prange->start, 512);

Instead of hard-coding 512 here, it would be more future-proof to call 
amdgpu_vm_pt_num_entries(adev, AMDGPU_VM_PDB0). That's currently a 
static function in amdgpu_vm_pt.c. Christian, would you object to 
making that non-static?

We don't have method to know if prange has huge page mapping which 
depends on virtual address 2MB align and physical address contiguous, it 
is decided inside amdgpu_vm_ptes_update. Even prange->start is not 2MB 
align, prange could have huge page mapping.

Regards,

Philip


Also, to improve the check whether the range can really use huge 
pages, you could add a check that it's size is at least 512 pages.



        if (!r) {
          list_add(&tail->list, insert_list);
-        if (!IS_ALIGNED(new_last + 1, 1UL << prange->granularity))
-            list_add(&tail->update_list, remap_list);
+        if (huge_page_mapping) {
+            if (!IS_ALIGNED(tail->start, 512))

Make that one condition: if (huge_page_mapping && !IS_ALIGNED...)


+ list_add(&tail->update_list, remap_list);
+        }
      }
      return r;
  }
@@ -1162,11 +1165,16 @@ svm_range_split_head(struct svm_range 
*prange, uint64_t new_start,
      struct svm_range *head = NULL;
      int r = svm_range_split(prange, new_start, prange->last, &head);
  +    bool huge_page_mapping = IS_ALIGNED(prange->start, 512);

Why the blank line before huge_page_mapping? It's part of your 
variable declarations.


+
      if (!r) {
          list_add(&head->list, insert_list);
-        if (!IS_ALIGNED(new_start, 1UL << prange->granularity))
-            list_add(&head->update_list, remap_list);
+        if (huge_page_mapping) {
+            if (!IS_ALIGNED(prange->start, 512))

Same as above.

Regards,
  Felix


+ list_add(&head->update_list, remap_list);
+        }
      }
+
      return r;
  }