[PATCH 4.13 10/43] s390/kvm: fix detection of guest machine checks

[Greg Kroah-Hartman]

4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

commit 0a5e2ec2647737907d267c09dc9a25fab1468865 upstream.

The new detection code for guest machine checks added a check based
on %r11 to .Lcleanup_sie to distinguish between normal asynchronous
interrupts and machine checks. But the funtion is called from the
program check handler as well with an undefined value in %r11.

The effect is that all program exceptions pointing to the SIE instruction
will set the CIF_MCCK_GUEST bit. The bit stays set for the CPU until the
 next machine check comes in which will incorrectly be interpreted as a
guest machine check.

The simplest fix is to stop using .Lcleanup_sie in the program check
handler and duplicate a few instructions.

Fixes: c929500d7a5a ("s390/nmi: s390: New low level handling for machine check happening in guest")
Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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
@@ -521,12 +521,15 @@ ENTRY(pgm_check_handler)
 	tmhh	%r8,0x0001		# test problem state bit
 	jnz	2f			# -> fault in user space
 #if IS_ENABLED(CONFIG_KVM)
-	# cleanup critical section for sie64a
+	# cleanup critical section for program checks in sie64a
 	lgr	%r14,%r9
 	slg	%r14,BASED(.Lsie_critical_start)
 	clg	%r14,BASED(.Lsie_critical_length)
 	jhe	0f
-	brasl	%r14,.Lcleanup_sie
+	lg	%r14,__SF_EMPTY(%r15)		# get control block pointer
+	ni	__SIE_PROG0C+3(%r14),0xfe	# no longer in SIE
+	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce
+	larl	%r9,sie_exit			# skip forward to sie_exit
 #endif
 0:	tmhh	%r8,0x4000		# PER bit set in old PSW ?
 	jnz	1f			# -> enabled, can't be a double fault