[PATCH] Xen/gntdev: don't ignore kernel unmapping error

[Jan Beulich <jbeulich@xxxxxxxx>]

While working on XSA-361 and its follow-ups, I failed to spot another
place where the kernel mapping part of an operation was not treated the
same as the user space part. Detect and propagate errors and add a 2nd
pr_debug().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
It is of course questionable whether zapping handles even upon failure
is the best course of action. Otoh unmapping shouldn't normally fail
unless there's a bug elsewhere (which is how I came to notice this
discrepancy).

--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -396,6 +396,14 @@ static int __unmap_grant_pages(struct gn
                        map->unmap_ops[offset+i].handle,
                        map->unmap_ops[offset+i].status);
                map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
+               if (use_ptemod) {
+                       if (map->kunmap_ops[offset+i].status)
+                               err = -EINVAL;
+                       pr_debug("kunmap handle=%u st=%d\n",
+                                map->kunmap_ops[offset+i].handle,
+                                map->kunmap_ops[offset+i].status);
+                       map->kunmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
+               }
        }
        return err;
 }