Re: [PATCH] kvm: x86: fix a race condition result to lost INIT

2017-07-30 19:33 GMT+08:00  [off-list ref]:

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2017-07-30 18:42 GMT+08:00  [off-list ref]:

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2017-07-31 0:24 GMT+08:00 Peng Hao [off-list ref]:

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when SMP VM start, AP may lost INIT because of receiving INIT between
kvm_vcpu_ioctl_x86_get/set_vcpu_events.

   vcpu 0                             vcpu 1
                               kvm_vcpu_ioctl_x86_get_vcpu_events
                                       events->smi.latched_init=0
 send INIT to vcpu1
   set vcpu1's pending_events
                               kvm_vcpu_ioctl_x86_set_vcpu_events
                                    events->smi.latched_init == 0
                                      clear INIT in pending_events
I don't think it need set/clear kernel state according to userspace's
info.

Signed-off-by: Peng Hao <redacted>
---
 arch/x86/kvm/x86.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c7266f..393a7b7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c

@@ -3157,12 +3157,6 @@ static int

kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
                        vcpu->arch.hflags |= HF_SMM_INSIDE_NMI_MASK;
                else
                        vcpu->arch.hflags &= ~HF_SMM_INSIDE_NMI_MASK;
-               if (lapic_in_kernel(vcpu)) {
-                       if (events->smi.latched_init)
-                               set_bit(KVM_APIC_INIT,
&vcpu->arch.apic->pending_events);

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This is not correct, you will lose the INIT after live migration. I
just send out another patch to fix it. Thanks for the report.

yes, you're right. I should modify on qemu not kernel.

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There is a patch here to fix it in kvm, https://lkml.org/lkml/2017/7/30/72

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I was affected by sipi, kernel never report  valid sipi to user space,

we don't care whether sipi is lost  after migration. Why?

Please refer to Paolo's suggestion,
https://www.mail-archive.com/qemu-devel@nongnu.org/msg464882.html

Regards,
Wanpeng Li

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-                       else
-                               clear_bit(KVM_APIC_INIT,
&vcpu->arch.apic->pending_events);
-               }
        }