Commit c0e7bb38 authored by Christian Borntraeger's avatar Christian Borntraeger Committed by Martin Schwidefsky
Browse files

s390/kvm: do not rely on the ILC on kvm host protection fauls 



For most cases a protection exception in the host (e.g. copy
on write or dirty tracking) on the sie instruction will indicate
an instruction length of 4. Turns out that there are some corner
cases (e.g. runtime instrumentation) where this is not necessarily
true and the ILC is unpredictable.

Let's replace our 4 byte rewind_pad with 3 byte nops to prepare for
all possible ILCs.

Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent b23afd38

arch/s390/kernel/entry.S

+13 −6
Original line number Diff line number Diff line
@@ -231,12 +231,17 @@ ENTRY(sie64a) 
	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

# interrupts. So lets use a nop (47 00 00 00) as a landing pad.

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

# are some corner cases (e.g. runtime instrumentation) where ILC is unpredictable.

# Other instructions between sie64a and .Lsie_done should not cause program

# interrupts. So lets use 3 nops as a landing pad for all possible rewinds.

# See also .Lcleanup_sie

.Lrewind_pad:

	nop	0

.Lrewind_pad6:

	nopr	7

.Lrewind_pad4:

	nopr	7

.Lrewind_pad2:

	nopr	7

	.globl sie_exit

sie_exit:

	lg	%r14,__SF_EMPTY+8(%r15)		# load guest register save area
@@ -249,7 +254,9 @@ sie_exit: 
	stg	%r14,__SF_EMPTY+16(%r15)	# set exit reason code

	j	sie_exit



	EX_TABLE(.Lrewind_pad,.Lsie_fault)

	EX_TABLE(.Lrewind_pad6,.Lsie_fault)

	EX_TABLE(.Lrewind_pad4,.Lsie_fault)

	EX_TABLE(.Lrewind_pad2,.Lsie_fault)

	EX_TABLE(sie_exit,.Lsie_fault)

EXPORT_SYMBOL(sie64a)

EXPORT_SYMBOL(sie_exit)

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