linux-kernel - Re: [PATCH v2 8/9] KVM: x86: lapic does not have to process INIT if it is blocked

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Date:   Wed, 17 Aug 2022 00:07:03 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        mlevitsk@...hat.com, vkuznets@...hat.com
Subject: Re: [PATCH v2 8/9] KVM: x86: lapic does not have to process INIT if
 it is blocked

On Thu, Aug 11, 2022, Paolo Bonzini wrote:
> Do not return true from kvm_apic_has_events, and consequently from
> kvm_vcpu_has_events, if the vCPU is not going to process an INIT.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/i8259.c            | 2 +-
>  arch/x86/kvm/lapic.h            | 2 +-
>  arch/x86/kvm/x86.c              | 5 +++++
>  arch/x86/kvm/x86.h              | 5 -----
>  5 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 293ff678fff5..1ce4ebc41118 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -2042,6 +2042,7 @@ void __user *__x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
>  				     u32 size);
>  bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu);
>  bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu);
> +bool kvm_vcpu_latch_init(struct kvm_vcpu *vcpu);
>  
>  bool kvm_intr_is_single_vcpu(struct kvm *kvm, struct kvm_lapic_irq *irq,
>  			     struct kvm_vcpu **dest_vcpu);
> diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
> index e1bb6218bb96..177555eea54e 100644
> --- a/arch/x86/kvm/i8259.c
> +++ b/arch/x86/kvm/i8259.c
> @@ -29,9 +29,9 @@
>  #include <linux/mm.h>
>  #include <linux/slab.h>
>  #include <linux/bitops.h>
> -#include "irq.h"
> +#include <linux/kvm_host.h>
>  
> -#include <linux/kvm_host.h>
> +#include "irq.h"
>  #include "trace.h"
>  
>  #define pr_pic_unimpl(fmt, ...)	\
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 117a46df5cc1..12577ddccdfc 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -225,7 +225,7 @@ static inline bool kvm_vcpu_apicv_active(struct kvm_vcpu *vcpu)
>  
>  static inline bool kvm_apic_has_events(struct kvm_vcpu *vcpu)
>  {
> -	return lapic_in_kernel(vcpu) && vcpu->arch.apic->pending_events;
> +	return lapic_in_kernel(vcpu) && vcpu->arch.apic->pending_events && !kvm_vcpu_latch_init(vcpu);

Blech, the kvm_apic_has_events() name is awful (as is pending_events), e.g. it
really should be kvm_apic_has_pending_sipi_or_init().

To avoid the odd kvm_vcpu_latch_init() declaration and the long line above, what
if we open code this in kvm_vcpu_has_events() like we do for NMI, SMI, etc...?

And as follow-up, I would love to rename kvm_vcpu_latch_init() => kvm_vcpu_init_blocked(),
kvm_apic_has_events(), and pending_events.

E.g. for this patch just do:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9f11b505cbee..559900736a71 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12533,7 +12533,8 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
        if (!list_empty_careful(&vcpu->async_pf.done))
                return true;

-       if (kvm_apic_has_events(vcpu))
+       /* comment explaning that SIPIs are dropped in this case. */
+       if (kvm_apic_has_events(vcpu) && !kvm_vcpu_latch_init(vcpu))
                return true;

        if (vcpu->arch.pv.pv_unhalted)