[PATCH 5.15] Ignore failure to unmap INVALID_GRANT_HANDLE

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

The error paths of gntdev_mmap() can call unmap_grant_pages() even
though not all of the pages have been successfully mapped.  This will
trigger the WARN_ON()s in __unmap_grant_pages_done().  The number of
warnings can be very large; I have observed thousands of lines of
warnings in the systemd journal.

Avoid this problem by only warning on unmapping failure if the handle
being unmapped is not INVALID_GRANT_HANDLE.  The handle field of any
page that was not successfully mapped will be INVALID_GRANT_HANDLE, so
this catches all cases where unmapping can legitimately fail.

Suggested-by: Juergen Gross <jgross@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
Fixes: 87a54feba68f ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
---
 drivers/xen/gntdev.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 
4b56c39f766d4da68570d08d963f6ef40c8d9c37..22fcd503f4a4487d0aed147c94f432683dad8c73
 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -396,13 +396,17 @@ static void __unmap_grant_pages_done(int result,
        unsigned int offset = data->unmap_ops - map->unmap_ops;
 
        for (i = 0; i < data->count; i++) {
-               WARN_ON(map->unmap_ops[offset+i].status);
+               WARN_ON(map->unmap_ops[offset+i].status &&
+                       map->unmap_ops[offset+i].handle !=
+                       INVALID_GRANT_HANDLE);
                pr_debug("unmap handle=%d st=%d\n",
                        map->unmap_ops[offset+i].handle,
                        map->unmap_ops[offset+i].status);
                map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
                if (use_ptemod) {
-                       WARN_ON(map->kunmap_ops[offset+i].status);
+                       WARN_ON(map->kunmap_ops[offset+i].status &&
+                               map->kunmap_ops[offset+i].handle !=
+                               INVALID_GRANT_HANDLE);
                        pr_debug("kunmap handle=%u st=%d\n",
                                 map->kunmap_ops[offset+i].handle,
                                 map->kunmap_ops[offset+i].status);
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab