linux-kernel - Re: [PATCH RFC V6 1/5] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

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Message-ID: <20120429132030.GB15413@redhat.com>
Date:	Sun, 29 Apr 2012 16:20:30 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alexander Graf <agraf@...e.de>,
	Randy Dunlap <rdunlap@...otime.net>, linux-doc@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	KVM <kvm@...r.kernel.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	X86 <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Xen <xen-devel@...ts.xensource.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC V6 1/5] kvm hypervisor : Add a hypercall to KVM
 hypervisor to support pv-ticketlocks

On Sun, Apr 29, 2012 at 04:18:03PM +0300, Avi Kivity wrote:
> On 04/24/2012 12:59 PM, Gleb Natapov wrote:
> > >  
> > > +/*
> > > + * kvm_pv_kick_cpu_op:  Kick a vcpu.
> > > + *
> > > + * @apicid - apicid of vcpu to be kicked.
> > > + */
> > > +static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
> > > +{
> > > +	struct kvm_vcpu *vcpu = NULL;
> > > +	int i;
> > > +
> > > +	kvm_for_each_vcpu(i, vcpu, kvm) {
> > > +		if (!kvm_apic_present(vcpu))
> > > +			continue;
> > > +
> > > +		if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
> > > +			break;
> > > +	}
> > > +	if (vcpu) {
> > > +		/*
> > > +		 * Setting unhalt flag here can result in spurious runnable
> > > +		 * state when unhalt reset does not happen in vcpu_block.
> > > +		 * But that is harmless since that should soon result in halt.
> > > +		 */
> > > +		vcpu->arch.pv.pv_unhalted = 1;
> > > +		/* We need everybody see unhalt before vcpu unblocks */
> > > +		smp_mb();
> > > +		kvm_vcpu_kick(vcpu);
> > > +	}
> > > +}
> > This is too similar to kvm_irq_delivery_to_apic(). Why not reuse it. We
> > can use one of reserved delivery modes as PV delivery mode. We will
> > disallow guest to trigger it through apic interface, so this will not be
> > part of ABI and can be changed at will.
> >
> 
> I'm not thrilled about this.  Those delivery modes will eventually
> become unreserved.  We can have a kvm_lookup_apic_id() that is shared
> among implementations.
> 
This is only internal implementation. If they become unreserved we will
use something else.

--
			Gleb.
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