linux-kernel - Re: [PATCH] KVM: x86: Add EOI_INDUCED exit handlers for Hyper-V SynIC vectors

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Date:   Thu, 7 Jul 2022 16:37:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Wang Guangju <wangguangju@...du.com>
Cc:     pbonzini@...hat.com, vkuznets@...hat.com, jmattson@...gle.com,
        wanpengli@...cent.com, bp@...en8.de, joro@...tes.org,
        suravee.suthikulpanit@....com, hpa@...or.com, tglx@...utronix.de,
        mingo@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, chukaiping <chukaiping@...du.com>
Subject: Re: [PATCH] KVM: x86: Add EOI_INDUCED exit handlers for Hyper-V
 SynIC vectors

This isn't adding a handler so much as it's signaling EOI for SynIC vectors. Maybe?

  KVM: x86: Send EOI to SynIC vectors on accelerated EOI-induced VM-Exits

On Thu, Jul 07, 2022, Wang Guangju wrote:
> From: chukaiping <chukaiping@...du.com>
> 
> When EOI virtualization is performed on VMX,
> kvm_apic_set_eoi_accelerated() is called upon
> EXIT_REASON_EOI_INDUCED but unlike its non-accelerated
> apic_set_eoi() sibling, Hyper-V SINT vectors are
> left unhandled.

Wrap changelogs closer to ~75 chars.

> This patch fix it, and add a new helper function to
> handle both IOAPIC and Hyper-V SINT vectors.

Avoid "this patch" and simply state what change is being made.  E.g.


  Send EOI to Hyper-V SINT vectors when handling acclerated EOI-induced
  VM-Exits.  KVM Hyper-V needs to handle the SINT EOI irrespective of
  whether the EOI is acclerated or not.

Fixes: 5c919412fe61 ("kvm/x86: Hyper-V synthetic interrupt controller")

and probably Cc: stable@...r.kernel.org?

> Suggested-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: wangguangju <wangguangju@...du.com>
> ---
>  arch/x86/kvm/lapic.c | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index f03facc..e046afe 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1269,6 +1269,16 @@ static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector)
>  	kvm_ioapic_update_eoi(apic->vcpu, vector, trigger_mode);
>  }
>  
> +static inline void apic_set_eoi_vector(struct kvm_lapic *apic, int vector)
> +{
> +	if (to_hv_vcpu(apic->vcpu) &&
> +	    test_bit(vector, to_hv_synic(apic->vcpu)->vec_bitmap))
> +		kvm_hv_synic_send_eoi(apic->vcpu, vector);
> +
> +	kvm_ioapic_send_eoi(apic, vector);
> +	kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
> +}

Rather than add a third helper, what about renaming kvm_apic_set_eoi_accelerated()
and having the non-accelerated helper call the "acclerated" version?  That will
document the delta between the non-accelerated patch and the accelerated path.
The only hiccup is tracing, but that's easy to resolve (or we could just not trace
if there's no valid vector to EOI), e.g.


/*
 * Send EOI for a valid vector.  The caller, or hardware when this is invoked
 * after an accelerated EOI VM-Exit, is responsible for updating the vISR and
 * vPPR.
 */
void kvm_apic_set_eoi(struct kvm_lapic *apic, int vector)
{
	trace_kvm_eoi(apic, vector);

	if (to_hv_vcpu(apic->vcpu) &&
	    test_bit(vector, to_hv_synic(apic->vcpu)->vec_bitmap))
		kvm_hv_synic_send_eoi(apic->vcpu, vector);

	kvm_ioapic_send_eoi(apic, vector);
	kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
}
EXPORT_SYMBOL_GPL(kvm_apic_set_eoi);

static int apic_set_eoi(struct kvm_lapic *apic)
{
	int vector = apic_find_highest_isr(apic);

	/*
	 * Not every write EOI will has corresponding ISR,
	 * one example is when Kernel check timer on setup_IO_APIC
	 */
	if (vector == -1) {
		trace_kvm_eoi(apic, vector);   <---- maybe just drop this?
		return vector;
	}

	apic_clear_isr(vector, apic);
	apic_update_ppr(apic);

	kvm_apic_set_eoi(apic, vector);

	return vector;
}