linux-kernel - Re: [PATCH 10/14] KVM: Split out a kvm_vcpu_block() helper from kvm_vcpu

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Message-ID: <16f057a7-5603-d4b1-266c-f9564b564f32@de.ibm.com>
Date:   Mon, 27 Sep 2021 09:41:59 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH 10/14] KVM: Split out a kvm_vcpu_block() helper from
 kvm_vcpu_halt()



Am 25.09.21 um 02:55 schrieb Sean Christopherson:
> Factor out the "block" part of kvm_vcpu_halt() so that x86 can emulate
> non-halt wait/sleep/block conditions that should not be subjected to
> halt-polling.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>

> ---
>   include/linux/kvm_host.h |  1 +
>   virt/kvm/kvm_main.c      | 50 ++++++++++++++++++++++++++++------------
>   2 files changed, 36 insertions(+), 15 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index d2a8be3fb9ba..655c2b24db2d 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -966,6 +966,7 @@ void kvm_sigset_activate(struct kvm_vcpu *vcpu);
>   void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);
>   
>   void kvm_vcpu_halt(struct kvm_vcpu *vcpu);
> +bool kvm_vcpu_block(struct kvm_vcpu *vcpu);
>   void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu);
>   void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu);
>   bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 280cf1dca7db..fe34457530c2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3199,6 +3199,34 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
>   	return ret;
>   }
>   
> +/*
> + * Block the vCPU until the vCPU is runnable, an event arrives, or a signal is
> + * pending.  This is mostly used when halting a vCPU, but may also be used
> + * directly for other vCPU non-runnable states, e.g. x86's Wait-For-SIPI.
> + */
> +bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
> +{
> +	bool waited = false;
> +
> +	kvm_arch_vcpu_blocking(vcpu);
> +
> +	prepare_to_rcuwait(&vcpu->wait);
> +	for (;;) {
> +		set_current_state(TASK_INTERRUPTIBLE);
> +
> +		if (kvm_vcpu_check_block(vcpu) < 0)
> +			break;
> +
> +		waited = true;
> +		schedule();
> +	}
> +	finish_rcuwait(&vcpu->wait);
> +
> +	kvm_arch_vcpu_unblocking(vcpu);
> +
> +	return waited;
> +}
> +
>   static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
>   					  ktime_t end, bool success)
>   {
> @@ -3221,6 +3249,12 @@ static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
>   	}
>   }
>   
> +/*
> + * Emulate a vCPU halt condition, e.g. HLT on x86, WFI on arm, etc...  If halt
> + * polling is enabled, busy wait for a short time before blocking to avoid the
> + * expensive block+unblock sequence if a wake event arrives soon after the vCPU
> + * is halted.
> + */
>   void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
>   {
>   	bool halt_poll_allowed = !kvm_arch_no_poll(vcpu);
> @@ -3245,21 +3279,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
>   		} while (kvm_vcpu_can_poll(cur, stop));
>   	}
>   
> -	kvm_arch_vcpu_blocking(vcpu);
> -
> -	prepare_to_rcuwait(&vcpu->wait);
> -	for (;;) {
> -		set_current_state(TASK_INTERRUPTIBLE);
> -
> -		if (kvm_vcpu_check_block(vcpu) < 0)
> -			break;
> -
> -		waited = true;
> -		schedule();
> -	}
> -	finish_rcuwait(&vcpu->wait);
> -
> -	kvm_arch_vcpu_unblocking(vcpu);
> +	waited = kvm_vcpu_block(vcpu);
>   
>   	cur = ktime_get();
>   	if (waited) {
>