This is a note to let you know that I've just added the patch titled
arm64: cmpxchg: Use "K" instead of "L" for ll/sc immediate constraint
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-cmpxchg-use-k-instead-of-l-for-ll-sc-immediate-constraint.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu Mar 4 02:48:46 PM CET 2021
From: Will Deacon <will.deacon@xxxxxxx>
Date: Tue, 18 Sep 2018 09:39:55 +0100
Subject: arm64: cmpxchg: Use "K" instead of "L" for ll/sc immediate constraint
From: Will Deacon <will.deacon@xxxxxxx>
commit 4230509978f2921182da4e9197964dccdbe463c3 upstream.
The "L" AArch64 machine constraint, which we use for the "old" value in
an LL/SC cmpxchg(), generates an immediate that is suitable for a 64-bit
logical instruction. However, for cmpxchg() operations on types smaller
than 64 bits, this constraint can result in an invalid instruction which
is correctly rejected by GAS, such as EOR W1, W1, #0xffffffff.
Whilst we could special-case the constraint based on the cmpxchg size,
it's far easier to change the constraint to "K" and put up with using
a register for large 64-bit immediates. For out-of-line LL/SC atomics,
this is all moot anyway.
Reported-by: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/atomic_ll_sc.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/include/asm/atomic_ll_sc.h
+++ b/arch/arm64/include/asm/atomic_ll_sc.h
@@ -268,7 +268,7 @@ __LL_SC_PREFIX(__cmpxchg_case_##name##sz
"2:" \
: [tmp] "=&r" (tmp), [oldval] "=&r" (oldval), \
[v] "+Q" (*(u##sz *)ptr) \
- : [old] "Lr" (old), [new] "r" (new) \
+ : [old] "Kr" (old), [new] "r" (new) \
: cl); \
\
return oldval; \
Patches currently in stable-queue which might be from will.deacon@xxxxxxx are
queue-4.19/arm64-cmpxchg-use-k-instead-of-l-for-ll-sc-immediate-constraint.patch
queue-4.19/arm64-avoid-redundant-type-conversions-in-xchg-and-cmpxchg.patch
