linux-kernel - Re: [RFC PATCH v5 076/104] KVM: x86: Add option to force LAPIC expiration wait

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Message-ID: <ad71b70b-34da-c14b-5cca-cf8a0b544050@redhat.com>
Date:   Tue, 5 Apr 2022 17:33:51 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 076/104] KVM: x86: Add option to force LAPIC
 expiration wait

On 3/4/22 20:49, isaku.yamahata@...el.com wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> Add an option to skip the IRR check-in kvm_wait_lapic_expire().  This
> will be used by TDX to wait if there is an outstanding notification for
> a TD, i.e. a virtual interrupt is being triggered via posted interrupt
> processing.  KVM TDX doesn't emulate PI processing, i.e. there will
> never be a bit set in IRR/ISR, so the default behavior for APICv of
> querying the IRR doesn't work as intended.

Would be better to explain "doesn't work as intended" more verbosely. 
Otherwise,

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo

> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>   arch/x86/kvm/lapic.c   | 4 ++--
>   arch/x86/kvm/lapic.h   | 2 +-
>   arch/x86/kvm/svm/svm.c | 2 +-
>   arch/x86/kvm/vmx/vmx.c | 2 +-
>   4 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 9322e6340a74..d49f029ef0e3 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1620,12 +1620,12 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
>   		__wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);
>   }
>   
> -void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
> +void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu, bool force_wait)
>   {
>   	if (lapic_in_kernel(vcpu) &&
>   	    vcpu->arch.apic->lapic_timer.expired_tscdeadline &&
>   	    vcpu->arch.apic->lapic_timer.timer_advance_ns &&
> -	    lapic_timer_int_injected(vcpu))
> +	    (force_wait || lapic_timer_int_injected(vcpu)))
>   		__kvm_wait_lapic_expire(vcpu);
>   }
>   EXPORT_SYMBOL_GPL(kvm_wait_lapic_expire);
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 2b44e533fc8d..2a0119ef9e96 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -233,7 +233,7 @@ static inline int kvm_lapic_latched_init(struct kvm_vcpu *vcpu)
>   
>   bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector);
>   
> -void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu);
> +void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu, bool force_wait);
>   
>   void kvm_bitmap_or_dest_vcpus(struct kvm *kvm, struct kvm_lapic_irq *irq,
>   			      unsigned long *vcpu_bitmap);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index c7eec23e9ebe..a46415845f48 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3766,7 +3766,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
>   	clgi();
>   	kvm_load_guest_xsave_state(vcpu);
>   
> -	kvm_wait_lapic_expire(vcpu);
> +	kvm_wait_lapic_expire(vcpu, false);
>   
>   	/*
>   	 * If this vCPU has touched SPEC_CTRL, restore the guest's value if
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 00f88aa25047..9b7bd52d19a9 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6838,7 +6838,7 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
>   	if (enable_preemption_timer)
>   		vmx_update_hv_timer(vcpu);
>   
> -	kvm_wait_lapic_expire(vcpu);
> +	kvm_wait_lapic_expire(vcpu, false);
>   
>   	/*
>   	 * If this vCPU has touched SPEC_CTRL, restore the guest's value if