Re: [PATCH RFC untested] kvm/x86: implement hv EOI assist

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Apr 23, 2014 at 01:12:49AM +0300, Michael S. Tsirkin wrote:
> On Tue, Apr 22, 2014 at 04:26:48PM -0300, Marcelo Tosatti wrote:
> > On Tue, Apr 22, 2014 at 12:11:47PM +0300, Michael S. Tsirkin wrote:
> > > On Mon, Apr 21, 2014 at 06:40:17PM -0300, Marcelo Tosatti wrote:
> > > > On Sun, Apr 13, 2014 at 04:10:22PM +0300, Michael S. Tsirkin wrote:
> > > > > It seems that it's easy to implement the EOI assist
> > > > > on top of the PV EOI feature: simply convert the
> > > > > page address to the format expected by PV EOI.
> > > > > 
> > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > > 
> > > > Looks alright except:
> > > > 
> > > > - There is no handling of PV EOI data to be performed at HV_X64_MSR_EOI write
> > > > path?
> 
> I thought HV_X64_MSR_EOI is a separate optimization - it's an X2APIC
> replacement that lets you do EOI with an MSR and not IO.
> No?

Yes.

> > > > - Migration fails with PV-EOI not enabled in CPUID ? (perhaps could
> > > >   require it for PV-EOI over HV-APIC-ASSIST).
> 
> Did not try migration yet - could you explain the issue please?
> HV-APIC-ASSIST MSR is in the list of saved MSRs ...

Restoration of MSR_KVM_PV_EOI_EN is required for migration under
when PVEOI enabled ?

> > > > - MS docs mention "No EOI required" is set only if interrupt injected is edge
> > > >   triggered.
> > > 
> > > Hmm I thought level interrupts are going through IOAPIC so that's already true isn't it?
> > > 
> > >         if (!pv_eoi_enabled(vcpu) ||
> > >             /* IRR set or many bits in ISR: could be nested. */
> > >             apic->irr_pending ||
> > >             /* Cache not set: could be safe but we don't bother. */
> > >             apic->highest_isr_cache == -1 ||
> > > --->        /* Need EOI to update ioapic. */
> > >             kvm_ioapic_handles_vector(vcpu->kvm, apic->highest_isr_cache)) {
> > 
> > Right.
> > 
> > >                 /*
> > >                  * PV EOI was disabled by apic_sync_pv_eoi_from_guest
> > >                  * so we need not do anything here.
> > >                  */
> > >                 return;
> > >         }
> > > 
> > > In any case if some interrupt handler ignores this bit because it's
> > > level, that's harmless since it will do EOI and then we'll clear the
> > > bit, right?
> > 
> > Yes.