Re: [PATCH] KVM: Don't mistreat edge-triggered INIT IPI as INIT de-assert. (LAPIC)

[Julian Stecklina <js@alien8.de>]

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Am Freitag, den 23.12.2011, 08:40 -0200 schrieb Marcelo Tosatti:
> On Mon, Dec 19, 2011 at 02:14:27AM +0100, Julian Stecklina wrote:
> > If the guest programs an IPI with level=0 (de-assert) and trig_mode=0 (edge),
> > it is erroneously treated as INIT de-assert and ignored, but to quote the
> > spec: "For this delivery mode [INIT de-assert], the level flag must be set to
> > 0 and trigger mode flag to 1."
> 
> Yes, the implementation ignores INIT de-assert. Quoting the spec:
> 
> "(INIT Level De-assert) (Not supported in the Pentium 4 and Intel Xeon
> processors.)"
> 
> Your patch below is not improving the implementation to be closer to the
> spec: it'll trigger the INIT state initialization with trig_mode == 0
> (which is not in accordance with your spec quote above).

After reading the spec again and consulting with the guy who wrote the
code triggering this, it seems the whole "if (level)" in the code path
below is superfluous. Regarding level my spec says:

"This flag has no meaning in Pentium 4 and Intel Xeon processors, and
will always be issued as a 1."

Judging from Section 10.2 this means every CPU where the LAPICs
communicate over the system bus (everything after and including the P4).
Thus the if can be removed, since its condition is always true
(regardless of what the programmer actually programmed into the level
field).

If there is no objection, I'll submit a revised patch.

> > Signed-off-by: Julian Stecklina <js@alien8.de>
> > ---
> >  arch/x86/kvm/lapic.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index a7f3e65..260770d 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -433,7 +433,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
> >  		break;
> >  
> >  	case APIC_DM_INIT:
> > -		if (level) {
> > +		if (!trig_mode || level) {
> >  			result = 1;
> >  			vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
> >  			kvm_make_request(KVM_REQ_EVENT, vcpu);
> > -- 
> > 1.7.7.4
> > 

Regards, Julian


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