Commit d5feec04 authored Feb 22, 2018 by Martin Schwidefsky

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>

parent 410d5e13

arch/s390/kernel/entry.S

+1 −0

Original line number	Original line	Diff line number	Diff line
	@@ -1440,6 +1440,7 @@ cleanup_critical:
	stg %r15,__LC_SYSTEM_TIMER		stg %r15,__LC_SYSTEM_TIMER
	0: # update accounting time stamp		0: # update accounting time stamp
	mvc __LC_LAST_UPDATE_TIMER(8),__LC_SYNC_ENTER_TIMER		mvc __LC_LAST_UPDATE_TIMER(8),__LC_SYNC_ENTER_TIMER
			BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
	# set up saved register r11		# set up saved register r11
	lg %r15,__LC_KERNEL_STACK		lg %r15,__LC_KERNEL_STACK
	la %r9,STACK_FRAME_OVERHEAD(%r15)		la %r9,STACK_FRAME_OVERHEAD(%r15)

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