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

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>

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index e23b5a0f31f2bcedb1e543f6845631125180183d..521c14c7a789366a2a4d0e4295faf21273d8699b 100644 (file)
--- 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,