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Date: Sat, 18 Dec 2021 09:08:39 +0000
From: "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)"
<longpeng2@...wei.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: "pbonzini@...hat.com" <pbonzini@...hat.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"Gonglei (Arei)" <arei.gonglei@...wei.com>,
Huangzhichao <huangzhichao@...wei.com>,
Wanpeng Li <wanpengli@...cent.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: The vcpu won't be wakened for a long time
> -----Original Message-----
> From: Sean Christopherson [mailto:seanjc@...gle.com]
> Sent: Thursday, December 16, 2021 11:43 PM
> To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> <longpeng2@...wei.com>
> Cc: pbonzini@...hat.com; kvm@...r.kernel.org; Gonglei (Arei)
> <arei.gonglei@...wei.com>; Huangzhichao <huangzhichao@...wei.com>; Wanpeng Li
> <wanpengli@...cent.com>; Vitaly Kuznetsov <vkuznets@...hat.com>; Jim Mattson
> <jmattson@...gle.com>; Joerg Roedel <joro@...tes.org>; linux-kernel
> <linux-kernel@...r.kernel.org>
> Subject: Re: The vcpu won't be wakened for a long time
>
> On Thu, Dec 16, 2021, Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> wrote:
> > > What kernel version? There have been a variety of fixes/changes in the
> > > area in recent kernels.
> >
> > The kernel version is 4.18, and it seems the latest kernel also has this problem.
> >
> > The following code can fixes this bug, I've tested it on 4.18.
> >
> > (4.18)
> >
> > @@ -3944,6 +3944,11 @@ static void vmx_deliver_posted_interrupt(struct
> kvm_vcpu *vcpu, int vector)
> > if (pi_test_and_set_on(&vmx->pi_desc))
> > return;
> >
> > + if (swq_has_sleeper(kvm_arch_vcpu_wq(vcpu))) {
> > + kvm_vcpu_kick(vcpu);
> > + return;
> > + }
> > +
> > if (vcpu != kvm_get_running_vcpu() &&
> > !kvm_vcpu_trigger_posted_interrupt(vcpu, false))
> > kvm_vcpu_kick(vcpu);
> >
> >
> > (latest)
> >
> > @@ -3959,6 +3959,11 @@ static int vmx_deliver_posted_interrupt(struct kvm_vcpu
> *vcpu, int vector)
> > if (pi_test_and_set_on(&vmx->pi_desc))
> > return 0;
> >
> > + if (rcuwait_active(&vcpu->wait)) {
> > + kvm_vcpu_kick(vcpu);
> > + return 0;
> > + }
> > +
> > if (vcpu != kvm_get_running_vcpu() &&
> > !kvm_vcpu_trigger_posted_interrupt(vcpu, false))
> > kvm_vcpu_kick(vcpu);
> >
> > Do you have any suggestions ?
>
> Hmm, that strongly suggests the "vcpu != kvm_get_running_vcpu()" is at fault.
> Can you try running with the below commit? It's currently sitting in kvm/queue,
> but not marked for stable because I didn't think it was possible for the check
> to a cause a missed wake event in KVM's current code base.
>
The below commit can fix the bug, we have just completed the tests.
Thanks.
> commit 6a8110fea2c1b19711ac1ef718680dfd940363c6
> Author: Sean Christopherson <seanjc@...gle.com>
> Date: Wed Dec 8 01:52:27 2021 +0000
>
> KVM: VMX: Wake vCPU when delivering posted IRQ even if vCPU == this vCPU
>
> Drop a check that guards triggering a posted interrupt on the currently
> running vCPU, and more importantly guards waking the target vCPU if
> triggering a posted interrupt fails because the vCPU isn't IN_GUEST_MODE.
> The "do nothing" logic when "vcpu == running_vcpu" works only because KVM
> doesn't have a path to ->deliver_posted_interrupt() from asynchronous
> context, e.g. if apic_timer_expired() were changed to always go down the
> posted interrupt path for APICv, or if the IN_GUEST_MODE check in
> kvm_use_posted_timer_interrupt() were dropped, and the hrtimer fired in
> kvm_vcpu_block() after the final kvm_vcpu_check_block() check, the vCPU
> would be scheduled() out without being awakened, i.e. would "miss" the
> timer interrupt.
>
> One could argue that invoking kvm_apic_local_deliver() from (soft) IRQ
> context for the current running vCPU should be illegal, but nothing in
> KVM actually enforces that rules. There's also no strong obvious benefit
> to making such behavior illegal, e.g. checking IN_GUEST_MODE and calling
> kvm_vcpu_wake_up() is at worst marginally more costly than querying the
> current running vCPU.
>
> Lastly, this aligns the non-nested and nested usage of triggering posted
> interrupts, and will allow for additional cleanups.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Message-Id: <20211208015236.1616697-18-seanjc@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 38749063da0e..f61a6348cffd 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3995,8 +3995,7 @@ static int vmx_deliver_posted_interrupt(struct kvm_vcpu
> *vcpu, int vector)
> * guaranteed to see PID.ON=1 and sync the PIR to IRR if triggering a
> * posted interrupt "fails" because vcpu->mode != IN_GUEST_MODE.
> */
> - if (vcpu != kvm_get_running_vcpu() &&
> - !kvm_vcpu_trigger_posted_interrupt(vcpu, false))
> + if (!kvm_vcpu_trigger_posted_interrupt(vcpu, false))
> kvm_vcpu_wake_up(vcpu);
>
> return 0;
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