KVM: s390: fix race in gmap_make_secure()

Fix a potential race in gmap_make_secure() and remove the last user of
follow_page() without FOLL_GET.

The old code is locking something it doesn't have a reference to, and
as explained by Jason and David in this discussion:
https://lore.kernel.org/linux-mm/Y9J4P%[email protected]/
it can lead to all kind of bad things, including the page getting
unmapped (MADV_DONTNEED), freed, reallocated as a larger folio and the
unlock_page() would target the wrong bit.
There is also another race with the FOLL_WRITE, which could race
between the follow_page() and the get_locked_pte().

The main point is to remove the last use of follow_page() without
FOLL_GET or FOLL_PIN, removing the races can be considered a nice
bonus.

Link: https://lore.kernel.org/linux-mm/Y9J4P%[email protected]/
Suggested-by: Jason Gunthorpe <[email protected]>
Fixes: 214d9bbcd3a6 ("s390/mm: provide memory management functions for protected KVM guests")
Reviewed-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Claudio Imbrenda <[email protected]>
Message-Id: <[email protected]>

0 files changed, 0 insertions, 0 deletions