On 11.07.22 02:05, Demi Marie Obenour wrote:

Hello Demi Marie

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@suse.com Cc: stable@vger.kernel.org Signed-off-by: Demi Marie Obenour demi@invisiblethingslab.com Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")

Reviewed-by: Oleksandr Tyshchenko oleksandr_tyshchenko@epam.com

---

drivers/xen/gntdev.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

Changes since v2:

• Use unmap_ops instead of kunmap_ops in the first WARN_ON

Changes since v1:

• Explicitly check for a status other than GNTST_okay instead of implicitly checking that it is nonzero.
• Avoid wrapping a line as within a comparison, as this makes the code hard to read.

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 4b56c39f766d4da68570d08d963f6ef40c8d9c37..84b143eef395b1585f3a8c0fdcb301ce9fbc52ec 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -396,13 +396,15 @@ 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 != GNTST_okay &&
  

• 	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 != GNTST_okay &&
  

• 		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);