> -----Original Message----- > From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: 29 March 2018 07:27 > To: Paul Durrant <paul.durr...@citrix.com> > Cc: Andrew Cooper <andrew.coop...@citrix.com>; xen-devel <xen- > de...@lists.xenproject.org> > Subject: RE: possible I/O emulation state machine issue > > >>> On 28.03.18 at 18:22, <paul.durr...@citrix.com> wrote: > >> From: Jan Beulich [mailto:jbeul...@suse.com] > >> Sent: 28 March 2018 16:59 > >> > >> 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. > > We do this only for actual MMIO accesses, not for RAM ones, > afaics. > > I think I see a way to deal with the specific case here, but we'll > certainly need to make things work properly in the general case. > That's not something reasonable to be done for 4.11 though. >
Page table modification racing with an emulation sounds pretty bad though. I guess that if the damage is only limited to the guest though it's not something that requires immediate fix. > Suppressing the stdvga port intercepts has, btw, not helped the > situation. > That surprises me. The whole string emulation should go out to QEMU without being broken up in that case, and since it's an outsw I don't see why there would be any retry of the linear->physical translation during completion. Paul > Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
