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Groups > linux.kernel > #1509776
| From | Radim Krčmář <rkrcmar@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 3/5] KVM: x86: do not use KVM_REQ_EVENT for APICv interrupt injection |
| Date | 2016-10-26 22:10 +0200 |
| Message-ID | <swCGl-a8-7@gated-at.bofh.it> (permalink) |
| References | <ssfoZ-4T2-9@gated-at.bofh.it> <ssfp0-4T2-31@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
2016-10-14 20:21+0200, Paolo Bonzini:
> Since bf9f6ac8d749 ("KVM: Update Posted-Interrupts Descriptor when vCPU
> is blocked", 2015-09-18) the posted interrupt descriptor is checked
> unconditionally for PIR.ON. Therefore we don't need KVM_REQ_EVENT to
> trigger the scan and, if NMIs or SMIs are not involved, we can avoid
> the complicated event injection path.
>
> Calling kvm_vcpu_kick if PIR.ON=1 is also useless, though it has been
> there since APICv was introduced.
>
> However, without the KVM_REQ_EVENT safety net KVM needs to be much
> more careful about races between vmx_deliver_posted_interrupt and
> vcpu_enter_guest. First, the IPI for posted interrupts may be issued
> between setting vcpu->mode = IN_GUEST_MODE and disabling interrupts.
> If that happens, kvm_trigger_posted_interrupt returns true, but
> smp_kvm_posted_intr_ipi doesn't do anything about it. The guest is
> entered with PIR.ON, but the posted interrupt IPI has not been sent
> and the interrupt is only delivered to the guest on the next vmentry
> (if any). To fix this, disable interrupts before setting vcpu->mode.
> This ensures that the IPI is delayed until the guest enters non-root mode;
> it is then trapped by the processor causing the interrupt to be injected.
>
> Second, the IPI may be issued between kvm_x86_ops->sync_pir_to_irr(vcpu)
> and vcpu->mode = IN_GUEST_MODE. In this case, kvm_vcpu_kick is called
> but it (correctly) doesn't do anything because it sees vcpu->mode ==
> OUTSIDE_GUEST_MODE. Again, the guest is entered with PIR.ON but no
> posted interrupt IPI is pending. This time, the fix for this is to move
> the PIR->IRR synchronization and RVI update after setting IN_GUEST_MODE.
>
> Both issues were previously masked by the liberal usage of KVM_REQ_EVENT.
> In both race scenarios KVM_REQ_EVENT would cancel guest entry, resulting
> in another vmentry which would inject the interrupt.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
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[PATCH 0/5] KVM: x86: cleanup and minimal speedup for APICv Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
[PATCH 3/5] KVM: x86: do not use KVM_REQ_EVENT for APICv interrupt injection Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 3/5] KVM: x86: do not use KVM_REQ_EVENT for APICv interrupt injection Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:10 +0200
[PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Wanpeng Li <kernellwp@gmail.com> - 2016-10-18 08:10 +0200
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:00 +0200
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 14:40 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-11-03 15:00 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 17:10 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 16:10 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 17:10 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 19:10 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-03 19:20 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 19:30 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-11-03 21:20 +0100
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-11-04 10:40 +0100
[PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 21:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Nadav Amit <nadav.amit@gmail.com> - 2016-10-14 21:50 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-15 09:50 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-16 04:40 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-10-19 20:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-27 00:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Nadav Amit <nadav.amit@gmail.com> - 2016-10-14 21:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-16 05:30 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-17 13:10 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-26 23:50 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-10-27 18:50 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-27 19:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-10-27 19:10 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-28 11:40 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-29 00:10 +0200
[PATCH 5/5] KVM: vmx: clear pending interrupts on KVM_SET_LAPIC Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 5/5] KVM: vmx: clear pending interrupts on KVM_SET_LAPIC Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:10 +0200
Re: [PATCH 0/5] KVM: x86: cleanup and minimal speedup for APICv "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-27 00:00 +0200
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