linux-kernel - Re: [RFC PATCH 06/18] KVM: Add facility to run guests on slave CPUs

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Message-ID: <4FEC8E22.4000208@redhat.com>
Date:	Thu, 28 Jun 2012 20:02:26 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	yrl.pp-manager.tt@...achi.com,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH 06/18] KVM: Add facility to run guests on slave CPUs

On 06/28/2012 09:07 AM, Tomoki Sekiyama wrote:
> Add path to migrate execution of vcpu_enter_guest to a slave CPU when
> vcpu->arch.slave_cpu is set.
> 
> After moving to the slave CPU, it goes back to the online CPU when the
> guest is exited by reasons that cannot be handled by the slave CPU only
> (e.g. handling async page faults).

What about, say, instruction emulation?  It may need to touch guest
memory, which cannot be done from interrupt disabled context.

> +
> +static int vcpu_post_run(struct kvm_vcpu *vcpu, struct task_struct *task,
> +			 int *can_complete_async_pf)
> +{
> +	int r = LOOP_ONLINE;
> +
> +	clear_bit(KVM_REQ_PENDING_TIMER, &vcpu->requests);
> +	if (kvm_cpu_has_pending_timer(vcpu))
> +		kvm_inject_pending_timer_irqs(vcpu);
> +
> +	if (dm_request_for_irq_injection(vcpu)) {
> +		r = -EINTR;
> +		vcpu->run->exit_reason = KVM_EXIT_INTR;
> +		++vcpu->stat.request_irq_exits;
> +	}
> +
> +	if (can_complete_async_pf) {
> +		*can_complete_async_pf = kvm_can_complete_async_pf(vcpu);
> +		if (r == LOOP_ONLINE)
> +			r = *can_complete_async_pf ? LOOP_APF : LOOP_SLAVE;
> +	} else
> +		kvm_check_async_pf_completion(vcpu);
> +
> +	if (signal_pending(task)) {
> +		r = -EINTR;
> +		vcpu->run->exit_reason = KVM_EXIT_INTR;
> +		++vcpu->stat.signal_exits;
> +	}

Isn't this racy?  The signal can come right after this.

-- 
error compiling committee.c: too many arguments to function


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