On 28/09/2016 12:04, Wu, Feng wrote: > > >> -----Original Message----- >> From: Paolo Bonzini [mailto:paolo.bonzini@xxxxxxxxx] On Behalf Of Paolo >> Bonzini >> Sent: Wednesday, September 28, 2016 5:20 AM >> To: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx >> Cc: yang.zhang.wz@xxxxxxxxx; Wu, Feng <feng.wu@xxxxxxxxx>; >> mst@xxxxxxxxxx; rkrcmar@xxxxxxxxxx >> Subject: [PATCH 2/3] kvm: x86: do not use KVM_REQ_EVENT for APICv interrupt >> injection >> >> 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. > > But the following code still remains in the KVM_REQ_EVENT checking part: > > if (kvm_lapic_enabled(vcpu)) { > update_cr8_intercept(vcpu); > kvm_lapic_sync_to_vapic(vcpu); > } > > Does this matter? Good question, but it doesn't matter for APICv because: - update_cr8_intercept is disabled if APICv, see vmx.c: if (enable_apicv) kvm_x86_ops->update_cr8_intercept = NULL; - kvm_lapic_sync_to_vapic's call to apic_sync_pv_eoi_to_guest is also disabled if APICv: if (!pv_eoi_enabled(vcpu) || apic->irr_pending || apic->highest_isr_cache == -1 || kvm_ioapic_handles_vector(apic, apic->highest_isr_cache)) return; (highest_isr_cache is always -1 for APICv) - The TPR/ISR/IRR shadow that kvm_lapic_sync_to_vapic writes is only read by the paravirtualized TPR access code in the vAPIC ROM (pc-bios/optionrom/kvmvapic.S in the QEMU tree). That code never runs if you don't get TPR access vmexits, and indeed TPR access vmexits never happen if KVM uses APICv (or even only the old-style TPR shadowing). Paolo > Thanks, > Feng > >> >> However, there is a race between vmx_deliver_posted_interrupt and >> vcpu_enter_guest. Fix it by disabling interrupts before vcpu->mode is >> set to IN_GUEST_MODE. >> >> Calling kvm_vcpu_kick if PIR.ON=1 is also useless, though it has been >> there since APICv was introduced. >> >> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> >> --- >> arch/x86/kvm/lapic.c | 2 -- >> arch/x86/kvm/vmx.c | 8 +++++--- >> arch/x86/kvm/x86.c | 9 +++++++-- >> 3 files changed, 12 insertions(+), 7 deletions(-) >> >> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >> index 63a442aefc12..be8b7ad56dd1 100644 >> --- a/arch/x86/kvm/lapic.c >> +++ b/arch/x86/kvm/lapic.c >> @@ -356,8 +356,6 @@ void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 >> *pir) >> struct kvm_lapic *apic = vcpu->arch.apic; >> >> __kvm_apic_update_irr(pir, apic->regs); >> - >> - kvm_make_request(KVM_REQ_EVENT, vcpu); >> } >> EXPORT_SYMBOL_GPL(kvm_apic_update_irr); >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index b33eee395b00..207b9aa32915 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -4844,9 +4844,11 @@ static void vmx_deliver_posted_interrupt(struct >> kvm_vcpu *vcpu, int vector) >> if (pi_test_and_set_pir(vector, &vmx->pi_desc)) >> return; >> >> - r = pi_test_and_set_on(&vmx->pi_desc); >> - kvm_make_request(KVM_REQ_EVENT, vcpu); >> - if (r || !kvm_vcpu_trigger_posted_interrupt(vcpu)) >> + /* If a previous notification has sent the IPI, nothing to do. */ >> + if (pi_test_and_set_on(&vmx->pi_desc)) >> + return; >> + >> + if (!kvm_vcpu_trigger_posted_interrupt(vcpu)) >> kvm_vcpu_kick(vcpu); >> } >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 3ee8a91a78c3..604cfbfc5bee 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -6658,6 +6658,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) >> kvm_x86_ops->prepare_guest_switch(vcpu); >> if (vcpu->fpu_active) >> kvm_load_guest_fpu(vcpu); >> + >> + /* >> + * Disable IRQs before setting IN_GUEST_MODE, so that >> + * posted interrupts with vcpu->mode == IN_GUEST_MODE >> + * always result in virtual interrupt delivery. >> + */ >> + local_irq_disable(); >> vcpu->mode = IN_GUEST_MODE; >> >> srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx); >> @@ -6671,8 +6678,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) >> */ >> smp_mb__after_srcu_read_unlock(); >> >> - local_irq_disable(); >> - >> if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests >> || need_resched() || signal_pending(current)) { >> vcpu->mode = OUTSIDE_GUEST_MODE; >> -- >> 1.8.3.1 >> > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
