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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 644/779] s390/smp: enforce lowcore protection on CPU restart
Date:   Mon, 15 Aug 2022 20:04:48 +0200
Message-Id: <20220815180404.884030334@linuxfoundation.org>
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From: Alexander Gordeev <agordeev@linux.ibm.com>

[ Upstream commit 6f5c672d17f583b081e283927f5040f726c54598 ]

As result of commit 915fea04f932 ("s390/smp: enable DAT before
CPU restart callback is called") the low-address protection bit
gets mistakenly unset in control register 0 save area of the
absolute zero memory. That area is used when manual PSW restart
happened to hit an offline CPU. In this case the low-address
protection for that CPU will be dropped.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Fixes: 915fea04f932 ("s390/smp: enable DAT before CPU restart callback is called")
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/s390/kernel/setup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 6b1a8697fae8..c8e7b3db82e2 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -507,8 +507,8 @@ static void __init setup_lowcore_dat_on(void)
 	S390_lowcore.svc_new_psw.mask |= PSW_MASK_DAT;
 	S390_lowcore.program_new_psw.mask |= PSW_MASK_DAT;
 	S390_lowcore.io_new_psw.mask |= PSW_MASK_DAT;
-	__ctl_store(S390_lowcore.cregs_save_area, 0, 15);
 	__ctl_set_bit(0, 28);
+	__ctl_store(S390_lowcore.cregs_save_area, 0, 15);
 	put_abs_lowcore(restart_flags, RESTART_FLAG_CTLREGS);
 	put_abs_lowcore(program_new_psw, lc->program_new_psw);
 	for (cr = 0; cr < ARRAY_SIZE(lc->cregs_save_area); cr++)
-- 
2.35.1