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KVM: X86: Fix softlockup when get the current kvmclock

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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>
This commit is contained in:
Wanpeng Li 2017-11-20 14:55:05 -08:00 committed by Paolo Bonzini
parent 12806ba937
commit e70b57a6ce
1 changed files with 7 additions and 4 deletions
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11
arch/x86/kvm/x86.c
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@ -1798,10 +1798,13 @@ u64 get_kvmclock_ns(struct kvm *kvm)
/* 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();