5.15-stable review patch. If anyone has any objections, please let me know.
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From: David Hildenbrand david@redhat.com
[ Upstream commit 3f29f6537f54d74e64bac0a390fb2e26da25800d ]
folio_wait_writeback() requires that no spinlocks are held and that a folio reference is held, as documented. After we dropped the PTL, the folio could get freed concurrently. So grab a temporary reference.
Fixes: 214d9bbcd3a6 ("s390/mm: provide memory management functions for protected KVM guests") Reviewed-by: Claudio Imbrenda imbrenda@linux.ibm.com Signed-off-by: David Hildenbrand david@redhat.com Link: https://lore.kernel.org/r/20240508182955.358628-2-david@redhat.com Signed-off-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Alexander Gordeev agordeev@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/s390/kernel/uv.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c index b54376c658688..4ec467605d328 100644 --- a/arch/s390/kernel/uv.c +++ b/arch/s390/kernel/uv.c @@ -299,6 +299,13 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb) rc = make_folio_secure(folio, uvcb); folio_unlock(folio); } + + /* + * Once we drop the PTL, the folio may get unmapped and + * freed immediately. We need a temporary reference. + */ + if (rc == -EAGAIN) + folio_get(folio); } unlock: pte_unmap_unlock(ptep, ptelock); @@ -311,6 +318,7 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb) * completion, this is just a useless check, but it is safe. */ folio_wait_writeback(folio); + folio_put(folio); } else if (rc == -EBUSY) { /* * If we have tried a local drain and the folio refcount