On Tue, Feb 04, 2014 at 03:12:43PM +0100, Andreas Färber wrote: > Am 03.02.2014 20:01, schrieb Eduardo Habkost: > > On Tue, Jan 21, 2014 at 05:13:50PM +0100, Paolo Bonzini wrote: > >> Il 21/01/2014 16:51, Andreas Färber ha scritto: > >>>>> We already do that for other bits (e.g. XSAVE/OSXSAVE), > >>> Please point me to the commit, a search for xsave did not come up with a > >>> commit changing such a thing - either it did not go through my queue or > >>> it slipped me through: Bugs are no excuse to produce more bugs. > >> > >> I meant that "-cpu SandyBridge" with TCG produces a CPU that doesn't > >> have XSAVE. > >> > >>>>> and in fact it > >>>>> is the same that we do for KVM: the KVM_GET_SUPPORTED_CPUID result is > >>>>> used to trim the generic feature bits. > >>> Our model definitions are the place to put stuff that real CPUs have. > >>> Either the CPU has it or it doesn't. If it does, then this patch is > >>> fully correct and it's TCG's job to mask things out. If we're adding > >>> artificial flags to the generic model definitions just to make KVM > >>> faster, then it is wrong - we have a choice of post_initialize and > >>> realize hooks for that. > >> > >> It would make TCG faster as well, and there would be no reason > >> really to avoid the "artificial" x2apic on TCG, if TCG implemented > >> x2apic at all. > > > > So, the discussion seem to have stalled. > > > > Andreas, are you still against the patch, after the arguments from Paolo > > and me? > > Yes, I am. I had proposed to discuss solutions at FOSDEM but Paolo was > not there, so no solution yet.
We have the weekly call tomorrow. Let's discuss there? > My main concern still is that if a CPU does not have a certain feature > we should not list it as one of its features but add it to its features > where sensible. Just because TCG filters it out today is not keeping > anyone from implementing it tomorrow, in which case the emulated CPUs > would suddenly gain the feature. Why is this a problem? We will just have to make sure features stay consistent for old -M machine types. > So my question still is, what rule can > we apply for enabling x2apic? (something like greater or equal this > family, etc. - then we can put it in your post_initialize hook so that > users can still override it) > > Regards, > Andreas > > -- > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany > GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
