Re: [Xen-devel] possible I/O emulation state machine issue

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 28 March 2018 16:59
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: RE: possible I/O emulation state machine issue
> 
> >>> On 28.03.18 at 15:48, <Paul.Durrant@xxxxxxxxxx> wrote:
> >>  -----Original Message-----
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: 26 March 2018 09:43
> >> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> >> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; xen-devel <xen-
> >> devel@xxxxxxxxxxxxxxxxxxxx>
> >> Subject: Re: possible I/O emulation state machine issue
> >>
> >> >>> On 23.03.18 at 14:41, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> > So somehow it appears the vcpu got back into guest and executed the
> next
> >> > instruction whilst there was pending I/O.
> >>
> >> Two new pieces of information, in case either rings a bell:
> >>
> >
> > Alas neither rings a bell.
> >
> >> The issue appears to never occur in hap=0 mode.
> >>
> >
> > That's quite an odd correlation.
> 
> Simply timing, perhaps. In any event, newest logs suggest we have
> an issue with Windows paging out the page the data for the
> REP OUTSW is coming from while the port I/O part of the operation
> is pending qemu's completion. Upon retry the linear->physical
> translation fails, and we leave incorrect state in place.
> 
> I thought we cache the translation result, thus avoiding the need
> for a translation during the retry cycle, so either I'm misremembering
> or this doesn't work as intended. And in fact doing the translation a
> second time (with the potential of it failing) is wrong here - when the
> port access has occurred, we must not fail the emulation anymore
> (repeating the port write would probably be fine for the VGA, but
> would hardly be fine for e.g. an IDE interface).
> 

Yes, I thought we made sure all reps were completed using cached translations 
before returning to guest.

  Paul

> Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel