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s390: do not bypass BPENTER for interrupt system calls 

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>
This commit is contained in:
Martin Schwidefsky 2018-02-22 13:42:29 +01:00
parent 410d5e13e7
commit d5feec04fe
1 changed files with 1 additions and 0 deletions
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arch/s390/kernel/entry.S
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@ -1440,6 +1440,7 @@ cleanup_critical:
stg %r15,__LC_SYSTEM_TIMER
0: # update accounting time stamp
mvc __LC_LAST_UPDATE_TIMER(8),__LC_SYNC_ENTER_TIMER
BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
# set up saved register r11
lg %r15,__LC_KERNEL_STACK
la %r9,STACK_FRAME_OVERHEAD(%r15)