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: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/entry.S

@@ -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