[ Upstream commit d5feec04fe578c8dbd9e2e1439afc2f0af761ed4 ]
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 --- arch/s390/kernel/entry.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index beda1c33ca12..2c71cdf2a4f0 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -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