From: Wanpeng Li <kernellwp@gmail.com>
Date: Mon, 20 Nov 2017 14:55:05 -0800
Subject: KVM: X86: Fix softlockup when get the current kvmclock
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Patch-mainline: v4.15-rc2
Git-commit: e70b57a6ce4e8b92a56a615ae79bdb2bd66035e7
References: bsc#1077761
watchdog: BUG: soft lockup - CPU#6 stuck for 22s! [qemu-system-x86:10185]
CPU: 6 PID: 10185 Comm: qemu-system-x86 Tainted: G OE 4.14.0-rc4+ #4
RIP: 0010:kvm_get_time_scale+0x4e/0xa0 [kvm]
Call Trace:
get_time_ref_counter+0x5a/0x80 [kvm]
kvm_hv_process_stimers+0x120/0x5f0 [kvm]
kvm_arch_vcpu_ioctl_run+0x4b4/0x1690 [kvm]
kvm_vcpu_ioctl+0x33a/0x620 [kvm]
do_vfs_ioctl+0xa1/0x5d0
SyS_ioctl+0x79/0x90
entry_SYSCALL_64_fastpath+0x1e/0xa9
This can be reproduced when running kvm-unit-tests/hyperv_stimer.flat and
cpu-hotplug stress simultaneously. __this_cpu_read(cpu_tsc_khz) returns 0
(set in kvmclock_cpu_down_prep()) when the pCPU is unhotplug which results
in kvm_get_time_scale() gets into an infinite loop.
This patch fixes it by treating the unhotplug pCPU as not using master clock.
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Alexander Graf <agraf@suse.de>
---
arch/x86/kvm/x86.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1798,10 +1798,13 @@
/* both __this_cpu_read() and rdtsc() should be on the same cpu */
get_cpu();
- kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
- &hv_clock.tsc_shift,
- &hv_clock.tsc_to_system_mul);
- ret = __pvclock_read_cycles(&hv_clock, rdtsc());
+ if (__this_cpu_read(cpu_tsc_khz)) {
+ kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
+ &hv_clock.tsc_shift,
+ &hv_clock.tsc_to_system_mul);
+ ret = __pvclock_read_cycles(&hv_clock, rdtsc());
+ } else
+ ret = ktime_get_boot_ns() + ka->kvmclock_offset;
put_cpu();