[PATCH V1] accel/amxdna: fix page-insertion errors in amdxdna_insert_pages()

[Lizhi Hou]

Two error paths in amdxdna_insert_pages() called vma->vm_ops->close(vma)
before returning an error code to the caller.  This is incorrect:
amdxdna_gem_obj_mmap() registers an HMM interval notifier before calling
amdxdna_insert_pages(), and on a hard error it jumps to hmm_unreg to undo
that registration.  Calling vm_ops->close() manually — which drops the
shmem pages_pin_count and the GEM object reference that backs the VMA —
before the mmap syscall has even returned causes those resources to be
released while the VMA is still alive.  The kernel VMA teardown will call
vm_ops->close() a second time when the process later unmaps the range,
producing a reference count underflow.

Replace both hard-error returns with a deferred-fault approach that keeps
the VMA alive and retries page insertion through the HMM range-fault path.

Fixes: e486147c912f ("accel/amdxdna: Add BO import and export")
Signed-off-by: Lizhi Hou <lizhi....@amd.com>
---
 drivers/accel/amdxdna/amdxdna_gem.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/accel/amdxdna/amdxdna_gem.c 
b/drivers/accel/amdxdna/amdxdna_gem.c
index d6fe6fb41286..aed110ad1c1e 100644
--- a/drivers/accel/amdxdna/amdxdna_gem.c
+++ b/drivers/accel/amdxdna/amdxdna_gem.c
@@ -435,6 +435,23 @@ static void amdxdna_gem_dev_obj_free(struct drm_gem_object 
*gobj)
        amdxdna_gem_destroy_obj(abo);
 }
 
+static void amdxdna_mark_mapp_invalid(struct amdxdna_gem_obj *abo,
+                                     struct vm_area_struct *vma)
+{
+       struct amdxdna_dev *xdna = to_xdna_dev(to_gobj(abo)->dev);
+       struct amdxdna_umap *mapp;
+
+       down_write(&xdna->notifier_lock);
+       abo->mem.map_invalid = true;
+       list_for_each_entry(mapp, &abo->mem.umap_list, node) {
+               if (compare_range(mapp, vma->vm_mm, vma->vm_start, 
vma->vm_end)) {
+                       mapp->invalid = true;
+                       break;
+               }
+       }
+       up_write(&xdna->notifier_lock);
+}
+
 static int amdxdna_insert_pages(struct amdxdna_gem_obj *abo,
                                struct vm_area_struct *vma)
 {
@@ -456,8 +473,7 @@ static int amdxdna_insert_pages(struct amdxdna_gem_obj *abo,
                                      &num_pages);
                if (ret) {
                        XDNA_ERR(xdna, "Failed insert pages %d", ret);
-                       vma->vm_ops->close(vma);
-                       return ret;
+                       amdxdna_mark_mapp_invalid(abo, vma);
                }
 
                return 0;
@@ -477,9 +493,9 @@ static int amdxdna_insert_pages(struct amdxdna_gem_obj *abo,
                fault_ret = handle_mm_fault(vma, vma->vm_start + offset,
                                            FAULT_FLAG_WRITE, NULL);
                if (fault_ret & VM_FAULT_ERROR) {
-                       vma->vm_ops->close(vma);
                        XDNA_ERR(xdna, "Fault in page failed");
-                       return -EFAULT;
+                       amdxdna_mark_mapp_invalid(abo, vma);
+                       break;
                }
 
                offset += PAGE_SIZE;
-- 
2.34.1