From: Martin Schwidefsky Date: Fri, 27 Apr 2018 05:36:55 +0000 (+0200) Subject: s390: do not bypass BPENTER for interrupt system calls X-Git-Tag: v4.4.130~31 X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=bbf89d7832ed4b94b7d689165f90dc38bba350ca;p=thirdparty%2Fkernel%2Fstable.git s390: do not bypass BPENTER for interrupt system calls [ 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 Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index beda1c33ca126..2c71cdf2a4f0a 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