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Subject[PATCH 5.4 099/168] s390/mm: fix panic in gup_fast on large pud
From: Gerald Schaefer <>

commit 582b4e55403e053d8a48ff687a05174da9cc3fb0 upstream.

On s390 there currently is no implementation of pud_write(). That was ok
as long as we had our own implementation of get_user_pages_fast() which
checked for pud protection by testing the bit directly w/o using
pud_write(). The other callers of pud_write() are not reachable on s390.

After commit 1a42010cdc26 ("s390/mm: convert to the generic
get_user_pages_fast code") we use the generic get_user_pages_fast(), which
does call pud_write() in pud_access_permitted() for FOLL_WRITE access on
a large pud. Without an s390 specific pud_write(), the generic version is
called, which contains a BUG() statement to remind us that we don't have a
proper implementation. This results in a kernel panic.

Fix this by providing an implementation of pud_write().

Cc: <> # 5.2+
Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code")
Signed-off-by: Gerald Schaefer <>
Reviewed-by: Heiko Carstens <>
Signed-off-by: Vasily Gorbik <>
Signed-off-by: Greg Kroah-Hartman <>

arch/s390/include/asm/pgtable.h | 6 ++++++
1 file changed, 6 insertions(+)

--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -756,6 +756,12 @@ static inline int pmd_write(pmd_t pmd)
return (pmd_val(pmd) & _SEGMENT_ENTRY_WRITE) != 0;

+#define pud_write pud_write
+static inline int pud_write(pud_t pud)
+ return (pud_val(pud) & _REGION3_ENTRY_WRITE) != 0;
static inline int pmd_dirty(pmd_t pmd)
int dirty = 1;

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