linux-kernel - Re: [v2 PATCH 3/4] x86/kvm: Add host side support for virtual suspend time injection

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Date:   Sat, 14 Aug 2021 09:22:18 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Hikaru Nishida <hikalium@...omium.org>,
        linux-kernel@...r.kernel.org, dme@....org, tglx@...utronix.de,
        mlevitsk@...hat.com
Cc:     suleiman@...gle.com, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        John Stultz <john.stultz@...aro.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>, kvm@...r.kernel.org,
        x86@...nel.org
Subject: Re: [v2 PATCH 3/4] x86/kvm: Add host side support for virtual suspend
 time injection

On 06/08/21 12:07, Hikaru Nishida wrote:
> +#if defined(CONFIG_KVM_VIRT_SUSPEND_TIMING) || \
> +	defined(CONFIG_KVM_VIRT_SUSPEND_TIMING_GUEST)
> +#define VIRT_SUSPEND_TIMING_VECTOR	0xec
> +#endif

No need to use a new vector.  You can rename the existing 
MSR_KVM_ASYNC_PF_INT to MSR_KVM_HYPERVISOR_CALLBACK_INT or something 
like that, and add the code to sysvec_kvm_asyncpf_interrupt.

> +static void kvm_make_suspend_time_interrupt(struct kvm_vcpu *vcpu)
> +{
> +	kvm_queue_interrupt(vcpu, VIRT_SUSPEND_TIMING_VECTOR, false);
> +	kvm_make_request(KVM_REQ_EVENT, vcpu);
> +}

Use kvm_apic_set_irq which will inject the interrupt as soon as 
possible, so you do not even need to check 
kvm_vcpu_ready_for_interrupt_injection.

> +#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING
> +		if (kvm->suspend_injection_requested &&
> +			kvm_vcpu_ready_for_interrupt_injection(vcpu)) {
> +			kvm_write_suspend_time(kvm);
> +			kvm_make_suspend_time_interrupt(vcpu);
> +			kvm->suspend_injection_requested = false;
> +		}
> +#endif

Do not read variables in vcpu_run; There is KVM_REQ_* if you need to do 
work in the vCPU run loop.

> +	mutex_lock(&kvm_lock);
> +	list_for_each_entry(kvm, &vm_list, vm_list) {
> +		if (!(kvm->arch.msr_suspend_time & KVM_MSR_ENABLED))
> +			continue;
> +
> +		kvm_for_each_vcpu(i, vcpu, kvm)
> +			vcpu->arch.tsc_offset_adjustment -= adj;
> +
> +		/*
> +		 * Move the offset of kvm_clock here as if it is stopped
> +		 * during the suspension.
> +		 */
> +		kvm->arch.kvmclock_offset -= suspend_time_ns;
> +
> +		/* suspend_time is accumulated per VM. */
> +		kvm->suspend_time_ns += suspend_time_ns;
> +		kvm->suspend_injection_requested = true;
> +		/*
> +		 * This adjustment will be reflected to the struct provided
> +		 * from the guest via MSR_KVM_HOST_SUSPEND_TIME before
> +		 * the notification interrupt is injected.
> +		 */
> +	}
> +	mutex_unlock(&kvm_lock);
> +}

As pointed out by Thomas, this should be a work item.

Paolo