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drm/amdkfd: Handle lack of READ permissions in SVM mapping

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HMM assumes that pages have READ permissions by default. Inside
svm_range_validate_and_map, we add READ permissions then add WRITE
permissions if the VMA isn't read-only. This will conflict with regions
that only have PROT_WRITE or have PROT_NONE. When that happens,
svm_range_restore_work will continue to retry, silently, giving the
impression of a hang if pr_debug isn't enabled to show the retries..

If pages don't have READ permissions, simply unmap them and continue. If
they weren't mapped in the first place, this would be a no-op. Since x86
doesn't support write-only, and PROT_NONE doesn't allow reads or writes
anyways, this will allow the svm range validation to continue without
getting stuck in a loop forever on mappings we can't use with HMM.

Signed-off-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Kent Russell
2025-07-21 14:06:36 -04:00
committed by Alex Deucher
parent 9d20f37a10
commit 0ed704d058
1 changed files with 23 additions and 0 deletions
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23
drivers/gpu/drm/amd/amdkfd/kfd_svm.c
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@@ -1713,6 +1713,29 @@ static int svm_range_validate_and_map(struct mm_struct *mm,
next = min(vma->vm_end, end);
npages = (next - addr) >> PAGE_SHIFT;
/* HMM requires at least READ permissions. If provided with PROT_NONE,
* unmap the memory. If it's not already mapped, this is a no-op
* If PROT_WRITE is provided without READ, warn first then unmap
*/
if (!(vma->vm_flags & VM_READ)) {
unsigned long e, s;
svm_range_lock(prange);
if (vma->vm_flags & VM_WRITE)
pr_debug("VM_WRITE without VM_READ is not supported");
s = max(start, prange->start);
e = min(end, prange->last);
if (e >= s)
r = svm_range_unmap_from_gpus(prange, s, e,
KFD_SVM_UNMAP_TRIGGER_UNMAP_FROM_CPU);
svm_range_unlock(prange);
/* If unmap returns non-zero, we'll bail on the next for loop
* iteration, so just leave r and continue
*/
addr = next;
continue;
}
WRITE_ONCE(p->svms.faulting_task, current);
r = amdgpu_hmm_range_get_pages(&prange->notifier, addr, npages,
readonly, owner, NULL,