Re: [Xen-devel] [PATCH 2/3] x86/nvmx: clarify and fix usage of nvmx_update_apicv

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Mar 24, 2020 at 11:33:00AM +0000, Tian, Kevin wrote:
> > From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > Sent: Tuesday, March 24, 2020 7:23 PM
> > 
> > On Tue, Mar 24, 2020 at 10:11:15AM +0000, Tian, Kevin wrote:
> > > > From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > > Sent: Tuesday, March 24, 2020 5:51 PM
> > > >
> > > > On Tue, Mar 24, 2020 at 06:03:28AM +0000, Tian, Kevin wrote:
> > > > > > From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> > > > > > Sent: Saturday, March 21, 2020 3:08 AM
> > > > > >
> > > > > > The current usage of nvmx_update_apicv is not clear: it is deeply
> > > > > > intertwined with the Ack interrupt on exit VMEXIT control.
> > > > > >
> > > > > > The code in nvmx_update_apicv should update the SVI (in service
> > > > interrupt)
> > > > > > field of the guest interrupt status only when the Ack interrupt on
> > > > > > exit is set, as it is used to record that the interrupt being
> > > > > > serviced is signaled in a vmcs field, and hence hasn't been injected
> > > > > > as on native. It's important to record the current in service
> > > > > > interrupt on the guest interrupt status field, or else further
> > > > > > interrupts won't respect the priority of the in service one.
> > > > > >
> > > > > > While clarifying the usage make sure that the SVI is only updated
> > when
> > > > > > Ack on exit is set and the nested vmcs interrupt info field is 
> > > > > > valid. Or
> > > > > > else a guest not using the Ack on exit feature would loose 
> > > > > > interrupts
> > as
> > > > > > they would be signaled as being in service on the guest interrupt
> > > > > > status field but won't actually be recorded on the interrupt info 
> > > > > > vmcs
> > > > > > field, neither injected in any other way.
> > > > >
> > > > > It is insufficient. You also need to update RVI to enable virtual 
> > > > > injection
> > > > > when Ack on exit is cleared.
> > > >
> > > > But RVI should be updated in vmx_intr_assist in that case, since
> > > > nvmx_intr_intercept shouldn't intercept the interrupt, as it should be
> > > > handled normally.
> > >
> > > As we discussed before, vmx_intr_assist is invoked before
> > nvmx_switch_guest.
> > >
> > > It is incorrectly to update RVI at that time since it might be still 
> > > vmcs02
> > being
> > > active (if no pending softirq to make it invoked again).
> > >
> > > Also nvmx_intr_intercept does intercept Ack-on-exit=0 case:
> > >
> > >         if ( intack.source == hvm_intsrc_pic ||
> > >                  intack.source == hvm_intsrc_lapic )

I've realized that nvmx_intr_intercept will return 1 for interrupts
originating from the lapic or the pic, while nvmx_update_apicv will
only update GUEST_INTR_STATUS for interrupts originating from the
lapic. Is this correct?

Shouldn't both be in sync and handle the same interrupt sources?

Thanks, Roger.