Re: [Xen-devel] [PATCH 3/3] x86/nvmx: update exit bitmap on vmexit

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

On Tue, Mar 24, 2020 at 06:22:43AM +0000, Tian, Kevin wrote:
> > From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> > Sent: Saturday, March 21, 2020 3:08 AM
> > 
> > Current code in nvmx_update_apicv set the guest interrupt status field
> > but doesn't update the exit bitmap, which can cause issues of lost
> > interrupts on the L1 hypervisor if vmx_intr_assist gets
> > short-circuited by nvmx_intr_intercept returning true.
> 
> Above is not accurate. Currently Xen didn't choose to update the EOI
> exit bitmap every time when there is a change. Instead, it chose to 
> batch the update before resuming to the guest. sort of optimization.
> So it is not related to whether SVI is changed. We should always do the 
> bitmap update in nvmx_update_apicv, regardless of the setting of
> Ack-on-exit ...

But if Ack on exit is not set the GUEST_INTR_STATUS won't be changed
by nvmx_intr_intercept, and hence there's no need to update the EOI
exit map?

If OTOH the GUEST_INTR_STATUS field is changed by vmx_intr_assist the
bitmap will already be updated there.

Thanks, Roger.