Commit 0a5e2ec2 authored Oct 05, 2017 by Martin Schwidefsky

s390/kvm: fix detection of guest machine checks

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: c929500d ("s390/nmi: s390: New low level handling for machine check happening in guest")
Cc: <stable@vger.kernel.org> # v4.13+
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent f3415787

arch/s390/kernel/entry.S

+5 −2

Original line number	Diff line number	Diff line
		@@ -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

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