From: Alexander Gordeev <agordeev@linux.ibm.com>
Date: Mon, 23 May 2022 12:38:14 +0200
Subject: s390/mcck: isolate SIE instruction when setting CIF_MCCK_GUEST flag
Git-commit: 29ccaa4b35ea874ddd50518e5c2c746b9238a792
Patch-mainline: v5.19-rc1
References: git-fixes

Commit d768bd892fc8 ("s390: add options to change branch prediction
behaviour for the kernel") introduced .Lsie_exit label - supposedly
to fence off SIE instruction. However, the corresponding address
range length .Lsie_crit_mcck_length was not updated, which led to
BPON code potentionally marked with CIF_MCCK_GUEST flag.

Both .Lsie_exit and .Lsie_crit_mcck_length were removed with commit
0b0ed657fe00 ("s390: remove critical section cleanup from entry.S"),
but the issue persisted - currently BPOFF and BPENTER macros might
get wrongly considered by the machine check handler as a guest.

Fixes: d768bd892fc8 ("s390: add options to change branch prediction behaviour for the kernel")
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
[ ptesarik: I'm updating .Lsie_crit_mcck_length here, because SLE12-SP5
  does not have upstream commit 0b0ed657fe003fdf4df3766b898e8869950aa1ce ]
Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 arch/s390/kernel/entry.S |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -281,7 +281,10 @@ ENTRY(sie64a)
 	BPEXIT	__SF_EMPTY+24(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST)
 .Lsie_entry:
 	sie	0(%r14)
-.Lsie_exit:
+# Let the next instruction be NOP to avoid triggering a machine check
+# and handling it in a guest as result of the instruction execution.
+	nopr	7
+.Lsie_leave:
 	BPOFF
 	BPENTER	__SF_EMPTY+24(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST)
 .Lsie_skip:
@@ -1444,7 +1447,7 @@ cleanup_critical:
 .Lsie_crit_mcck_start:
 	.quad   .Lsie_entry
 .Lsie_crit_mcck_length:
-	.quad   .Lsie_skip - .Lsie_entry
+	.quad   .Lsie_leave - .Lsie_entry
 #endif
 
 	.section .rodata, "a"