Mailing List Archive

commit d501ef90ae7f2a79130ea89acb3d6d1792972934
Author: Julien Grall <jgrall@amazon.com>
AuthorDate: Wed Jul 29 14:50:37 2020 +0100
Commit: Julien Grall <jgrall@amazon.com>
CommitDate: Fri Aug 14 20:21:23 2020 +0100

xen/arm: cmpxchg: Add missing memory barriers in __cmpxchg_mb_timeout()

The function __cmpxchg_mb_timeout() was intended to have the same
semantics as __cmpxchg_mb(). Unfortunately, the memory barriers were
not added when first implemented.

There is no known issue with the existing callers, but the barriers are
added given this is the expected semantics in Xen.

The issue was introduced by XSA-295.

Backport: 4.8+
Fixes: 86b0bc958373 ("xen/arm: cmpxchg: Provide a new helper that can timeout")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
---
xen/include/asm-arm/arm32/cmpxchg.h | 8 +++++++-
xen/include/asm-arm/arm64/cmpxchg.h | 8 +++++++-
2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/xen/include/asm-arm/arm32/cmpxchg.h b/xen/include/asm-arm/arm32/cmpxchg.h
index 49ca2a0d7a..0770f272ee 100644
--- a/xen/include/asm-arm/arm32/cmpxchg.h
+++ b/xen/include/asm-arm/arm32/cmpxchg.h
@@ -147,7 +147,13 @@ static always_inline bool __cmpxchg_mb_timeout(volatile void *ptr,
int size,
unsigned int max_try)
{
- return __int_cmpxchg(ptr, old, new, size, true, max_try);
+ bool ret;
+
+ smp_mb();
+ ret = __int_cmpxchg(ptr, old, new, size, true, max_try);
+ smp_mb();
+
+ return ret;
}

#define cmpxchg(ptr,o,n) \
diff --git a/xen/include/asm-arm/arm64/cmpxchg.h b/xen/include/asm-arm/arm64/cmpxchg.h
index 5bc2e1f786..fc5c60f0bd 100644
--- a/xen/include/asm-arm/arm64/cmpxchg.h
+++ b/xen/include/asm-arm/arm64/cmpxchg.h
@@ -160,7 +160,13 @@ static always_inline bool __cmpxchg_mb_timeout(volatile void *ptr,
int size,
unsigned int max_try)
{
- return __int_cmpxchg(ptr, old, new, size, true, max_try);
+ bool ret;
+
+ smp_mb();
+ ret = __int_cmpxchg(ptr, old, new, size, true, max_try);
+ smp_mb();
+
+ return ret;
}

#define cmpxchg(ptr, o, n) \
--
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