The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 60f1bf29c0b2519989927cae640cd1f50f59dc7f Mon Sep 17 00:00:00 2001

From: David Hildenbrand david@redhat.com Date: Fri, 11 Jan 2019 15:18:22 +0100 Subject: [PATCH] s390/smp: Fix calling smp_call_ipl_cpu() from ipl CPU

When calling smp_call_ipl_cpu() from the IPL CPU, we will try to read from pcpu_devices->lowcore. However, due to prefixing, that will result in reading from absolute address 0 on that CPU. We have to go via the actual lowcore instead.

This means that right now, we will read lc->nodat_stack == 0 and therfore work on a very wrong stack.

This BUG essentially broke rebooting under QEMU TCG (which will report a low address protection exception). And checking under KVM, it is also broken under KVM. With 1 VCPU it can be easily triggered.

:/# echo 1 > /proc/sys/kernel/sysrq :/# echo b > /proc/sysrq-trigger [ 28.476745] sysrq: SysRq : Resetting [ 28.476793] Kernel stack overflow. [ 28.476817] CPU: 0 PID: 424 Comm: sh Not tainted 5.0.0-rc1+ #13 [ 28.476820] Hardware name: IBM 2964 NE1 716 (KVM/Linux) [ 28.476826] Krnl PSW : 0400c00180000000 0000000000115c0c (pcpu_delegate+0x12c/0x140) [ 28.476861] R:0 T:1 IO:0 EX:0 Key:0 M:0 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3 [ 28.476863] Krnl GPRS: ffffffffffffffff 0000000000000000 000000000010dff8 0000000000000000 [ 28.476864] 0000000000000000 0000000000000000 0000000000ab7090 000003e0006efbf0 [ 28.476864] 000000000010dff8 0000000000000000 0000000000000000 0000000000000000 [ 28.476865] 000000007fffc000 0000000000730408 000003e0006efc58 0000000000000000 [ 28.476887] Krnl Code: 0000000000115bfe: 4170f000 la %r7,0(%r15) [ 28.476887] 0000000000115c02: 41f0a000 la %r15,0(%r10) [ 28.476887] #0000000000115c06: e370f0980024 stg %r7,152(%r15) [ 28.476887] >0000000000115c0c: c0e5fffff86e brasl %r14,114ce8 [ 28.476887] 0000000000115c12: 41f07000 la %r15,0(%r7) [ 28.476887] 0000000000115c16: a7f4ffa8 brc 15,115b66 [ 28.476887] 0000000000115c1a: 0707 bcr 0,%r7 [ 28.476887] 0000000000115c1c: 0707 bcr 0,%r7 [ 28.476901] Call Trace: [ 28.476902] Last Breaking-Event-Address: [ 28.476920] [<0000000000a01c4a>] arch_call_rest_init+0x22/0x80 [ 28.476927] Kernel panic - not syncing: Corrupt kernel stack, can't continue. [ 28.476930] CPU: 0 PID: 424 Comm: sh Not tainted 5.0.0-rc1+ #13 [ 28.476932] Hardware name: IBM 2964 NE1 716 (KVM/Linux) [ 28.476932] Call Trace:

Fixes: 2f859d0dad81 ("s390/smp: reduce size of struct pcpu") Cc: stable@vger.kernel.org # 4.0+ Reported-by: Cornelia Huck cohuck@redhat.com Signed-off-by: David Hildenbrand david@redhat.com Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 307a1c86ea21..b198ece2aad6 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -381,8 +381,13 @@ void smp_call_online_cpu(void (*func)(void *), void *data) */ void smp_call_ipl_cpu(void (*func)(void *), void *data) { + struct lowcore *lc = pcpu_devices->lowcore; + + if (pcpu_devices[0].address == stap()) + lc = &S390_lowcore; + pcpu_delegate(&pcpu_devices[0], func, data, - pcpu_devices->lowcore->nodat_stack); + lc->nodat_stack); }

int smp_find_processor_id(u16 address)