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s390: do not bypass BPENTER for interrupt system calls

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[ Upstream commit d5feec04fe ]

The system call path can be interrupted before the switch back to the
standard branch prediction with BPENTER has been done. The critical
section cleanup code skips forward to .Lsysc_do_svc and bypasses the
BPENTER. In this case the kernel and all subsequent code will run with
the limited branch prediction.

Fixes: eacf67eb9b32 ("s390: run user space and KVM guests with modified branch prediction")
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Martin Schwidefsky
2018-04-27 07:36:55 +02:00
committed by Greg Kroah-Hartman
parent f3303788c0
commit bbf89d7832
1 changed files with 2 additions and 1 deletions
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3
arch/s390/kernel/entry.S
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@@ -1299,7 +1299,8 @@ cleanup_critical:
srag %r9,%r9,23
jz 0f
mvc __TI_last_break(8,%r12),16(%r11)
0: # set up saved register r11
0: BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
# set up saved register r11
lg %r15,__LC_KERNEL_STACK
la %r9,STACK_FRAME_OVERHEAD(%r15)
stg %r9,24(%r11) # r11 pt_regs pointer