So turns out a Linux guest with Q35 and OVMF can work with npt on or off. However a Linux guest with i440fx only works with npt disabled.
I'll follow the iommu mailing list for updates with regards to NPT affecting GPU FPS performance. On 18 Apr 2017 16:14, "Nick Sarnie" <commendsar...@gmail.com> wrote: > On Tue, Apr 18, 2017 at 10:09 AM, Graham Neville > <grahamnevi...@gmail.com> wrote: > > Has there been any feedback on this at all? > > > > I'm still struggling to get a Windows and Linux VM working at the same > time > > with npt=1. Annoying as I'm having to reboot in to a different kernel if > I > > want to use one or the other. > > > > Are you able to share your Kernel command line and XML for the Linux host > > please? > > > > > > On 7 Apr 2017 22:54, "Nick Sarnie" <commendsar...@gmail.com> wrote: > > > > I can't reproduce that issue, I tested a Fedora VM with both npt 0 and > > 1, of course with the same GPU performance results as windows. I've > > mailed some AMD guys and KVM guys, and hopefully someone can at least > > figure out what is going on. Also, Alex has reproduced this himself on > > both Nvidia and AMD GPUs. > > > > On Fri, Apr 7, 2017 at 5:49 PM, Graham Neville <grahamnevi...@gmail.com> > > wrote: > >> Sarnex, > >> > >> I have similar oddities with npt with Ryzen. As you say with > kvm-amd.npt=0 > >> the GPU performance is so much better (In my Witcher3 tests I'm going > from > >> 40fps to 75fps!). However with npt disabled the Windows10 VM slows down > an > >> awful lot in general tasks. > >> > >> I've also noticed that I can only run a Linux guest with kvm-amd.npt=0, > if > >> I > >> have it set to enabled then the Linux guest fails to start. I have the > >> same > >> issue even just trying to install Linux from an ISO, it will crash at > the > >> GRUB install menu. > >> > >> Hopefully someone knows a fix for this. > >> > >> _______________________________________________ > >> vfio-users mailing list > >> vfio-users@redhat.com > >> https://www.redhat.com/mailman/listinfo/vfio-users > >> > > > > > > Alex emailed Paolo, the KVM maintainer, some traces but he couldn't > find anything in them. Please follow the thread on the iommu mailing > list for more details. For now, I think we have to disable NPT. >
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