[PATCH v2] KVM: s390: fix gisa destroy operation might lead to cpu stalls

Michael Mueller
2023-08-24T13:12:07Z

A GISA cannot be destroyed as long it is linked in the GIB alert list
as this would breake the alert list. Just waiting for its removal from
the list triggered by another vm is not sufficient as it might be the
only vm. The below shown cpu stall situation might occur when GIB alerts
are delayed and is fixed by calling process_gib_alert_list() instead of
waiting.

At this time the vcpus of the vm are already destroyed and thus
no vcpu can be kicked to enter the SIE again if for some reason an
interrupt is pending for that vm.

Additianally the IAM restore value ist set to 0x00 if that was not the
case. That would be a bug introduced by incomplete device de-registration,
i.e. missing kvm_s390_gisc_unregister() call.

Setting this value guarantees that late interrupts don't bring the GISA
back into the alert list.

Both situation can now be observed in the kvm-trace:

00 01692880424:653210 3 - 0004 000003ff80136b58 vm 0x000000008e588000 created by pid 3019
00 01692880472:159783 3 - 0002 000003ff80143c06 vm 0x000000008e588000 has unexpected restore iam 0x02
00 01692880472:159784 3 - 0002 000003ff80143c24 vm 0x000000008e588000 gisa in alert list during destroy
00 01692880472:229846 3 - 0004 000003ff8013319a vm 0x000000008e588000 destroyed

CPU stall caused by kvm_s390_gisa_destroy():

[ 4915.311372] rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 14-.... } 24533 jiffies s: 5269 root: 0x1/.
[ 4915.311390] rcu: blocking rcu_node structures (internal RCU debug): l=1:0-15:0x4000/.
[ 4915.311394] Task dump for CPU 14:
[ 4915.311395] task:qemu-system-s39 state:R running task stack:0 pid:217198 ppid:1 flags:0x00000045
[ 4915.311399] Call Trace:
[ 4915.311401] [<0000038003a33a10>] 0x38003a33a10
[ 4933.861321] rcu: INFO: rcu_sched self-detected stall on CPU
[ 4933.861332] rcu: 14-....: (42008 ticks this GP) idle=53f4/1/0x4000000000000000 softirq=61530/61530 fqs=14031
[ 4933.861353] rcu: (t=42008 jiffies g=238109 q=100360 ncpus=18)
[ 4933.861357] CPU: 14 PID: 217198 Comm: qemu-system-s39 Not tainted 6.5.0-20230816.rc6.git26.a9d17c5d8813.300.fc38.s390x #1
[ 4933.861360] Hardware name: IBM 8561 T01 703 (LPAR)
[ 4933.861361] Krnl PSW : 0704e00180000000 000003ff804bfc66 (kvm_s390_gisa_destroy+0x3e/0xe0 [kvm])
[ 4933.861414] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
[ 4933.861416] Krnl GPRS: 0000000000000000 00000372000000fc 00000002134f8000 000000000d5f5900
[ 4933.861419] 00000002f5ea1d18 00000002f5ea1d18 0000000000000000 0000000000000000
[ 4933.861420] 00000002134fa890 00000002134f8958 000000000d5f5900 00000002134f8000
[ 4933.861422] 000003ffa06acf98 000003ffa06858b0 0000038003a33c20 0000038003a33bc8
[ 4933.861430] Krnl Code: 000003ff804bfc58: ec66002b007e cij %r6,0,6,000003ff804bfcae
000003ff804bfc5e: b904003a lgr %r3,%r10
#000003ff804bfc62: a7f40005 brc 15,000003ff804bfc6c
>000003ff804bfc66: e330b7300204 lg %r3,10032(%r11)
000003ff804bfc6c: 58003000 l %r0,0(%r3)
000003ff804bfc70: ec03fffb6076 crj %r0,%r3,6,000003ff804bfc66
000003ff804bfc76: e320b7600271 lay %r2,10080(%r11)
000003ff804bfc7c: c0e5fffea339 brasl %r14,000003ff804942ee
[ 4933.861444] Call Trace:
[ 4933.861445] [<000003ff804bfc66>] kvm_s390_gisa_destroy+0x3e/0xe0 [kvm]
[ 4933.861460] ([<00000002623523de>] free_unref_page+0xee/0x148)
[ 4933.861507] [<000003ff804aea98>] kvm_arch_destroy_vm+0x50/0x120 [kvm]
[ 4933.861521] [<000003ff8049d374>] kvm_destroy_vm+0x174/0x288 [kvm]
[ 4933.861532] [<000003ff8049d4fe>] kvm_vm_release+0x36/0x48 [kvm]
[ 4933.861542] [<00000002623cd04a>] __fput+0xea/0x2a8
[ 4933.861547] [<00000002620d5bf8>] task_work_run+0x88/0xf0
[ 4933.861551] [<00000002620b0aa6>] do_exit+0x2c6/0x528
[ 4933.861556] [<00000002620b0f00>] do_group_exit+0x40/0xb8
[ 4933.861557] [<00000002620b0fa6>] __s390x_sys_exit_group+0x2e/0x30
[ 4933.861559] [<0000000262d481f4>] __do_syscall+0x1d4/0x200
[ 4933.861563] [<0000000262d59028>] system_call+0x70/0x98
[ 4933.861565] Last Breaking-Event-Address:
[ 4933.861566] [<0000038003a33b60>] 0x38003a33b60

Fixes: 9f30f6216378 ("KVM: s390: add gib_alert_irq_handler()")
Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
---
arch/s390/kvm/interrupt.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 85e39f472bb4..06890a58d001 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -3216,11 +3216,15 @@ void kvm_s390_gisa_destroy(struct kvm *kvm)

if (!gi->origin)
return;
- if (gi->alert.mask)
- KVM_EVENT(3, "vm 0x%pK has unexpected iam 0x%02x",
+ if (gi->alert.mask) {
+ KVM_EVENT(3, "vm 0x%pK has unexpected restore iam 0x%02x",
kvm, gi->alert.mask);
- while (gisa_in_alert_list(gi->origin))
- cpu_relax();
+ gi->alert.mask = 0x00;
+ }
+ if (gisa_in_alert_list(gi->origin)) {
+ KVM_EVENT(3, "vm 0x%pK gisa in alert list during destroy", kvm);
+ process_gib_alert_list();
+ }
hrtimer_cancel(&gi->timer);
gi->origin = NULL;
VM_EVENT(kvm, 3, "gisa 0x%pK destroyed", gisa);
--
2.34.1