RE: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set

[Wu, Feng]

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx
> [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Paolo Bonzini
> Sent: Thursday, December 18, 2014 1:43 AM
> To: Wu, Feng; Thomas Gleixner; Ingo Molnar; H. Peter Anvin; x86@xxxxxxxxxx;
> Gleb Natapov; Paolo Bonzini; dwmw2@xxxxxxxxxxxxx; joro@xxxxxxxxxx; Alex
> Williamson; Jiang Liu
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; KVM list;
> Eric Auger
> Subject: Re: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set
> 
> 
> 
> On 12/12/2014 16:14, Feng Wu wrote:
> > Currently, we don't support urgent interrupt, all interrupts
> > are recognized as non-urgent interrupt, so we cannot send
> > posted-interrupt when 'SN' is set.
> 
> Can this happen?  If the vcpu is in guest mode, it cannot have been
> scheduled out, and that's the only case when SN is set.
> 
> Paolo

Currently, the only place where SN is set is vCPU is preempted and waiting for
the next scheduling in the runqueue. But I am not sure whether we need to
set SN for other purpose in future. Adding SN checking here is just to follow
the Spec. non-urgent interrupts are suppressed when SN is set.

Thanks,
Feng

> 
> > Signed-off-by: Feng Wu
> <feng.wu-ral2JQCrhuEAvxtiuMwx3w@xxxxxxxxxxxxxxxx>
> > ---
> >  arch/x86/kvm/vmx.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index a1c83a2..0aee151 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -4401,15 +4401,22 @@ static int vmx_vm_has_apicv(struct kvm *kvm)
> >  static void vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int
> vector)
> >  {
> >  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> > -	int r;
> > +	int r, sn;
> >
> >  	if (pi_test_and_set_pir(vector, &vmx->pi_desc))
> >  		return;
> >
> > +	/*
> > +	 * Currently, we don't support urgent interrupt, all interrupts
> > +	 * are recognized as non-urgent interrupt, so we cannot send
> > +	 * posted-interrupt when 'SN' is set.
> > +	 */
> > +	sn = pi_test_sn(&vmx->pi_desc);
> > +
> >  	r = pi_test_and_set_on(&vmx->pi_desc);
> >  	kvm_make_request(KVM_REQ_EVENT, vcpu);
> >  #ifdef CONFIG_SMP
> > -	if (!r && (vcpu->mode == IN_GUEST_MODE))
> > +	if (!r && !sn && (vcpu->mode == IN_GUEST_MODE))
> >  		apic->send_IPI_mask(get_cpu_mask(vcpu->cpu),
> >  				POSTED_INTR_VECTOR);
> >  	else
> > --
> --
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