On Thu, 04 May 2017 16:32:59 +0200 Andrea Bolognani <abolo...@redhat.com> wrote:
> On Thu, 2017-04-27 at 17:28 +1000, David Gibson wrote: > > This is a rebased and revised version of my patches revising CPU > > compatiblity mode handling on ppc, last posted in November. Since > > then, many of the patches have already been merged (some for 2.9, some > > since). This is what's left. > > > > * There was conceptual confusion about what a compatibility mode > > means, and how it interacts with the machine type. This cleans > > that up, clarifying that a compatibility mode (as an externally set > > option) only makes sense on machine types that don't permit the > > guest hypervisor privilege (i.e. 'pseries') > > > > * It was previously the user's (or management layer's) responsibility > > to determine compatibility of CPUs on either end for migration. > > This uses the compatibility modes to check that properly during an > > incoming migration. > > I started playing with this, mostly with libvirt integration > in mind of course, and quickly ran into a behavior that I > believe was not intentional and unfortunately managed to slip > into 2.9, I assume through the patches which were initially > part of this series (mentioned above). > > More specifically, when I run a guest with > > -M pseries-2.8 -cpu host > > using QEMU 2.8, the CPU in the guest is reported as > > POWER8E (raw), altivec supported > > However, when using QEMU 2.9 with the very same command line, > including explicitly using the pseries-2.8 machine type, I > get > > POWER8 (architected), altivec supported > The goal of this series is indeed to switch from raw to architected but I agree that it shouldn't affect existing machine types. This probably calls for some compat prop. > instead. The same happens with current master + your patches > applied on top. > > I'm not sure how much real trouble that will actually cause > for guests, but it's a guest-visible change as a result of > upgrading QEMU, which should just not happen. > > > I'll keep testing your series and get back to you as soon as > I have more feedback or questions. > > -- > Andrea Bolognani / Red Hat / Virtualization >
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