linux-kernel - [PATCH AUTOSEL 6.6 3/5] s390/stackleak: Use exrl instead of ex in __stackleak

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Message-Id: <20250126144906.925468-3-sashal@kernel.org>
Date: Sun, 26 Jan 2025 09:49:04 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Sven Schnelle <svens@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Sasha Levin <sashal@...nel.org>,
	gor@...ux.ibm.com,
	imbrenda@...ux.ibm.com,
	meted@...ux.ibm.com,
	linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 6.6 3/5] s390/stackleak: Use exrl instead of ex in __stackleak_poison()

From: Sven Schnelle <svens@...ux.ibm.com>

[ Upstream commit a88c26bb8e04ee5f2678225c0130a5fbc08eef85 ]

exrl is present in all machines currently supported, therefore prefer
it over ex. This saves one instruction and doesn't need an additional
register to hold the address of the target instruction.

Signed-off-by: Sven Schnelle <svens@...ux.ibm.com>
Reviewed-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/s390/include/asm/processor.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index e7338ed540d8f..2f373e8cfed33 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -140,8 +140,7 @@ static __always_inline void __stackleak_poison(unsigned long erase_low,
 		"	la	%[addr],256(%[addr])\n"
 		"	brctg	%[tmp],0b\n"
 		"1:	stg	%[poison],0(%[addr])\n"
-		"	larl	%[tmp],3f\n"
-		"	ex	%[count],0(%[tmp])\n"
+		"	exrl	%[count],3f\n"
 		"	j	4f\n"
 		"2:	stg	%[poison],0(%[addr])\n"
 		"	j	4f\n"
-- 
2.39.5