[PATCH V3] accel/amdxdna: Set HMM_PFN_REQ_WRITE for writable BO faults

[Lizhi Hou]

When aie2_populate_range() faults in pages, it only sets
HMM_PFN_REQ_FAULT. Without HMM_PFN_REQ_WRITE, handle_mm_fault() does not
request write permissions and may populate the CPU page tables with
read-only PTEs.

Check the VMA flags and set HMM_PFN_REQ_WRITE when the VMA has VM_WRITE.

Fixes: e486147c912f ("accel/amdxdna: Add BO import and export")
Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxx>
---
V3:
  Revert the V2 change. Instead, add comment to describe why it is not
an issue.
V2:
  Fix sashiko comment.

 drivers/accel/amdxdna/amdxdna_gem.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
index e861db6f9369..a5e30855c8a1 100644
--- a/drivers/accel/amdxdna/amdxdna_gem.c
+++ b/drivers/accel/amdxdna/amdxdna_gem.c
@@ -418,7 +418,15 @@ static int amdxdna_hmm_register(struct amdxdna_gem_obj *abo,
 	mapp->range.notifier = &mapp->notifier;
 	mapp->range.start = vma->vm_start;
 	mapp->range.end = vma->vm_end;
+	/*
+	 * Access permissions are fixed at mmap() time. Changing them later
+	 * with mprotect() is not supported: the range keeps requesting the
+	 * original permissions, so the application may see a fault failure
+	 * or an IOMMU fault.
+	 */
 	mapp->range.default_flags = HMM_PFN_REQ_FAULT;
+	if (vma->vm_flags & VM_WRITE)
+		mapp->range.default_flags |= HMM_PFN_REQ_WRITE;
 	mapp->abo = abo;
 	kref_init(&mapp->refcnt);
 
-- 
2.34.1