Re: [Xen-devel] [PATCHv2] x86info: dump kvm cpuid's

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Wed, May 02, 2012 at 10:45:27AM +0100, Ian Campbell wrote:
> On Tue, 2012-05-01 at 16:04 +0300, Gleb Natapov wrote:
> > > BTW, according to arch/x86/include/asm/kvm_para.h unsurprisingly KVM has
> > > a signature too 'KVMKVMKVM'.
> > > 
> > > >         cpu->stepping = eax & 0xf;
> > > >         cpu->model = (eax >> 4) & 0xf;
> > > >         cpu->family = (eax >> 8) & 0xf;
> > > > @@ -29,6 +29,19 @@ void get_cpu_info_basics(struct cpudata *cpu)
> > > >  
> > > >         cpuid(cpu->number, 0xC0000000, &maxei, NULL, NULL, NULL);
> > > >         cpu->maxei2 = maxei;
> > > > +       if (ecx & 0x80000000) {
> > > > +               cpuid(cpu->number, 0x40000000, &maxhv, NULL, NULL, 
> > > > NULL);
> > > > +               /*
> > > > +                * KVM up to linux 3.4 reports 0 as the max hypervisor 
> > > > leaf,
> > > > +                * where it really means 0x40000001.
> > > 
> > > This is something where I definitely think you want to check the
> > > signature first.
> > In theory yes, but in practice what will this break?
> 
> I've got no idea -- but what's the harm in checking?
> 
> Ian.

Users can set kvm signature to anything, if they do
debugging will be a bit harder for them.

> -- 
> Ian Campbell
> Current Noise: Hypocrisy - Roswell 47
> 
> Angels we have heard on High
> Tell us to go out and Buy.
>               -- Tom Lehrer

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