linux-kernel - Re: [PATCH v2 4/5] KVM: X86: TSCDEADLINE MSR emulation fastpath

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Message-ID: <1309372a-0dcf-cba6-9d65-e50139bbe46b@redhat.com>
Date:   Thu, 23 Apr 2020 11:37:00 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v2 4/5] KVM: X86: TSCDEADLINE MSR emulation fastpath

On 23/04/20 11:01, Wanpeng Li wrote:
> +
> +void kvm_set_lapic_tscdeadline_msr(struct kvm_vcpu *vcpu, u64 data)
> +{
> +	if (__kvm_set_lapic_tscdeadline_msr(vcpu, data))
> +		start_apic_timer(vcpu->arch.apic);
> +}
> +
> +int kvm_set_lapic_tscdeadline_msr_fast(struct kvm_vcpu *vcpu, u64 data)
> +{
> +	struct kvm_lapic *apic = vcpu->arch.apic;
> +
> +	if (__kvm_set_lapic_tscdeadline_msr(vcpu, data)) {
> +		atomic_set(&apic->lapic_timer.pending, 0);
> +		if (start_hv_timer(apic))
> +			return tscdeadline_expired_timer_fast(vcpu);
> +	}
> +
> +	return 1;
>  }
>
> +static int tscdeadline_expired_timer_fast(struct kvm_vcpu *vcpu)
> +{
> +	if (kvm_check_request(KVM_REQ_PENDING_TIMER, vcpu)) {
> +		kvm_clear_request(KVM_REQ_PENDING_TIMER, vcpu);
> +		kvm_inject_apic_timer_irqs_fast(vcpu);
> +		atomic_set(&vcpu->arch.apic->lapic_timer.pending, 0);
> +	}
> +
> +	return 0;
> +}

This could also be handled in apic_timer_expired.  For example you can
add an argument from_timer_fn and do

	if (!from_timer_fn) {
		WARN_ON(kvm_get_running_vcpu() != vcpu);
		kvm_inject_apic_timer_irqs_fast(vcpu);
		return;
	}

        if (kvm_use_posted_timer_interrupt(apic->vcpu)) {
                ...
	}
	atomic_inc(&apic->lapic_timer.pending);
	kvm_set_pending_timer(vcpu);

and then you don't need kvm_set_lapic_tscdeadline_msr_fast and
everything else.  Anyway thanks, this is already much better.

Paoo