On 2025-08-08 16:28, Kent Russell wrote:
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.russ...@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehl...@amd.com>
---
drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index e23b5a0f31f2..521c14c7a789 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -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,
