Re: [PATCH v2 2/2] KVM: nVMX: fix acknowledge interrupt on exit when APICv is in use

From: Wanpeng Li
Date: Tue Aug 05 2014 - 08:43:04 EST

On Tue, Aug 05, 2014 at 02:39:05PM +0200, Felipe Reyes wrote:
>Hi,
>
>On 08/05/2014 01:04 PM, Paolo Bonzini wrote:
>>Il 05/08/2014 06:42, Wanpeng Li ha scritto:
>>>After commit 77b0f5d (KVM: nVMX: Ack and write vector info to intr_info
>>>if L1 asks us to), "Acknowledge interrupt on exit" behavior can be
>>>emulated. To do so, KVM will ask the APIC for the interrupt vector if
>>>during a nested vmexit if VM_EXIT_ACK_INTR_ON_EXIT is set. With APICv,
>>>kvm_get_apic_interrupt would return -1 and give the following WARNING:
>>>
>>>Call Trace:
>>> [<ffffffff81493563>] dump_stack+0x49/0x5e
>>> [<ffffffff8103f0eb>] warn_slowpath_common+0x7c/0x96
>>> [<ffffffffa059709a>] ? nested_vmx_vmexit+0xa4/0x233 [kvm_intel]
>>> [<ffffffff8103f11a>] warn_slowpath_null+0x15/0x17
>>> [<ffffffffa059709a>] nested_vmx_vmexit+0xa4/0x233 [kvm_intel]
>>> [<ffffffffa0594295>] ? nested_vmx_exit_handled+0x6a/0x39e [kvm_intel]
>>> [<ffffffffa0537931>] ? kvm_apic_has_interrupt+0x80/0xd5 [kvm]
>>> [<ffffffffa05972ec>] vmx_check_nested_events+0xc3/0xd3 [kvm_intel]
>>> [<ffffffffa051ebe9>] inject_pending_event+0xd0/0x16e [kvm]
>>> [<ffffffffa051efa0>] vcpu_enter_guest+0x319/0x704 [kvm]
>>>
>>>If enabling APIC-v, all interrupts to L1 are delivered through APIC-v.
>>>But when L2 is running, external interrupt will casue L1 vmexit with
>>>reason external interrupt. Then L1 will pick up the interrupt through
>>>vmcs12. when L1 ack the interrupt, since the APIC-v is enabled when
>>>L1 is running, so APIC-v hardware still will do vEOI updating. The problem
>>>is that the interrupt is delivered not through APIC-v hardware, this means
>>>SVI/RVI/vPPR are not setting, but hardware required them when doing vEOI
>>>updating. The solution is that, when L1 tried to pick up the interrupt
>>>from vmcs12, then hypervisor will help to update the SVI/RVI/vPPR to make
>>>sure the following vEOI updating and vPPR updating corrently.
>>>
>>>Also, since interrupt is delivered through vmcs12, so APIC-v hardware will
>>>not cleare vIRR and hypervisor need to clear it before L1 running.
>>>
>>>Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>>>Suggested-by: "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>
>>>Tested-by: Liu, RongrongX <rongrongx.liu@xxxxxxxxx>
>>>Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
>>>---
>>>v1 -> v2:
>>> * reusing kvm_get_apic_interrupt here (by modifying kvm_cpu_get_interrupt,
>>> apic_set_isr and apic_clear_irr)
>>>
>>> arch/x86/kvm/irq.c | 2 +-
>>> arch/x86/kvm/lapic.c | 52 +++++++++++++++++++++++++++++++++++++++-------------
>>> 2 files changed, 40 insertions(+), 14 deletions(-)
>>>
>>>diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
>>>index bd0da43..a1ec6a5 100644
>>>--- a/arch/x86/kvm/irq.c
>>>+++ b/arch/x86/kvm/irq.c
>>>@@ -108,7 +108,7 @@ int kvm_cpu_get_interrupt(struct kvm_vcpu *v)
>>>
>>> vector = kvm_cpu_get_extint(v);
>>>
>>>- if (kvm_apic_vid_enabled(v->kvm) || vector != -1)
>>>+ if (vector != -1)
>>> return vector; /* PIC */
>>>
>>> return kvm_get_apic_interrupt(v); /* APIC */
>>>diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>>>index 3855103..08e8a89 100644
>>>--- a/arch/x86/kvm/lapic.c
>>>+++ b/arch/x86/kvm/lapic.c
>>>@@ -352,25 +352,46 @@ static inline int apic_find_highest_irr(struct kvm_lapic *apic)
>>>
>>> static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)
>>> {
>>>- apic->irr_pending = false;
>>>+ struct kvm_vcpu *vcpu;
>>>+
>>>+ vcpu = apic->vcpu;
>>>+
>>> apic_clear_vector(vec, apic->regs + APIC_IRR);
>>>- if (apic_search_irr(apic) != -1)
>>>- apic->irr_pending = true;
>>>+ if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
>>>+ /* try to update RVI */
>>>+ kvm_make_request(KVM_REQ_EVENT, vcpu);
>>>+ else {
>>>+ vec = apic_search_irr(apic);
>>>+ apic->irr_pending = (vec != -1);
>>>+ }
>>> }
>>>
>>> static inline void apic_set_isr(int vec, struct kvm_lapic *apic)
>>> {
>>>- /* Note that we never get here with APIC virtualization enabled. */
>>>+ struct kvm_vcpu *vcpu;
>>>+
>>>+ if (__apic_test_and_set_vector(vec, apic->regs + APIC_ISR))
>>>+ return;
>>>+
>>>+ vcpu = apic->vcpu;
>>>
>>>- if (!__apic_test_and_set_vector(vec, apic->regs + APIC_ISR))
>>>- ++apic->isr_count;
>>>- BUG_ON(apic->isr_count > MAX_APIC_VECTOR);
>>> /*
>>>- * ISR (in service register) bit is set when injecting an interrupt.
>>>- * The highest vector is injected. Thus the latest bit set matches
>>>- * the highest bit in ISR.
>>>+ * With APIC virtualization enabled, all caching is disabled
>>>+ * because the processor can modify ISR under the hood. Instead
>>>+ * just set SVI.
>>> */
>>>- apic->highest_isr_cache = vec;
>>>+ if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
>>>+ kvm_x86_ops->hwapic_isr_update(vcpu->kvm, vec);
>>>+ else {
>>>+ ++apic->isr_count;
>>>+ BUG_ON(apic->isr_count > MAX_APIC_VECTOR);
>>>+ /*
>>>+ * ISR (in service register) bit is set when injecting an interrupt.
>>>+ * The highest vector is injected. Thus the latest bit set matches
>>>+ * the highest bit in ISR.
>>>+ */
>>>+ apic->highest_isr_cache = vec;
>>>+ }
>>> }
>>>
>>> static inline int apic_find_highest_isr(struct kvm_lapic *apic)
>>>@@ -1627,11 +1648,16 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
>>> int vector = kvm_apic_has_interrupt(vcpu);
>>> struct kvm_lapic *apic = vcpu->arch.apic;
>>>
>>>- /* Note that we never get here with APIC virtualization enabled. */
>>>-
>>> if (vector == -1)
>>> return -1;
>>>
>>>+ /*
>>>+ * We get here even with APIC virtualization enabled, if doing
>>>+ * nested virtualization and L1 runs with the "acknowledge interrupt
>>>+ * on exit" mode. Then we cannot inject the interrupt via RVI,
>>>+ * because the process would deliver it through the IDT.
>>>+ */
>>>+
>>> apic_set_isr(vector, apic);
>>> apic_update_ppr(apic);
>>> apic_clear_irr(vector, apic);
>>>
>>
>>Thanks, this looks good. Felipe, can you test this patch together with
>>http://article.gmane.org/gmane.linux.kernel/1762356/raw please?
>>
>>Paolo
>>
>
>I checked that the bug was still there using the latest version of
>linus' kernel (8e099d1) and it is, then I applied the patches you
>indicated and the problem went away. So those 2 patches fix the
>problem for me.
>

Thanks for your verify.

Regards,
Wanpeng Li

>Best,
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