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Commit dcd2a9aa authored by Martin Schwidefsky's avatar Martin Schwidefsky
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s390/kvm: fix interrupt race with HANDLE_SIE_INTERCEPT 



The HANDLE_SIE_INTERCEPT macro is used in the interrupt handlers
and the program check handler to undo a few changes done by sie64a.
Among them are guest vs host LPP, the gmap ASCE vs kernel ASCE and
the bit that indicates that SIE is currently running on the CPU.

There is a race of a voluntary SIE exit vs asynchronous interrupts.
If the CPU completed the SIE instruction and the TM instruction of
the LPP macro at the time it receives an interrupt, the interrupt
handler will run while the LPP, the ASCE and the SIE bit are still
set up for guest execution. This might result in wrong sampling data,
but it will not cause data corruption or lockups.

The critical section in sie64a needs to be enlarged to include all
instructions that undo the changes required for guest execution.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent d05377c1

arch/s390/kernel/entry.S

+4 −10
Original line number Diff line number Diff line
@@ -90,14 +90,7 @@ _PIF_WORK = (_PIF_PER_TRAP) 
	lgr	\scratch,%r9

	slg	\scratch,BASED(.Lsie_critical)

	clg	\scratch,BASED(.Lsie_critical_length)

	.if	\reason==1

	# Some program interrupts are suppressing (e.g. protection).

	# We must also check the instruction after SIE in that case.

	# do_protection_exception will rewind to .Lrewind_pad

	jh	.+42

	.else

	jhe	.+42

	.endif

	lg	%r14,__SF_EMPTY(%r15)		# get control block pointer

	LPP	__SF_EMPTY+16(%r15)		# set host id

	ni	__SIE_PROG0C+3(%r14),0xfe	# no longer in SIE
@@ -1308,15 +1301,16 @@ ENTRY(sie64a) 
	lg	%r14,__SF_EMPTY(%r15)		# get control block pointer

	oi	__SIE_PROG0C+3(%r14),1		# we are going into SIE now

	tm	__SIE_PROG20+3(%r14),3		# last exit...

	jnz	.Lsie_done

	jnz	.Lsie_skip

	tm	__LC_CPU_FLAGS+7,_CIF_FPU

	jo	.Lsie_done			# exit if fp/vx regs changed

	jo	.Lsie_skip			# exit if fp/vx regs changed

	LPP	__SF_EMPTY(%r15)		# set guest id

	sie	0(%r14)

.Lsie_done:

	LPP	__SF_EMPTY+16(%r15)		# set host id

.Lsie_skip:

	ni	__SIE_PROG0C+3(%r14),0xfe	# no longer in SIE

	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce

.Lsie_done:

# some program checks are suppressing. C code (e.g. do_protection_exception)

# will rewind the PSW by the ILC, which is 4 bytes in case of SIE. Other

# instructions between sie64a and .Lsie_done should not cause program