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

[Gleb Natapov <gleb@xxxxxxxxxx>]

On Tue, May 01, 2012 at 01:27:05PM +0100, Ian Campbell wrote:
> On Mon, 2012-04-30 at 17:38 +0300, Michael S. Tsirkin wrote:
> > The following makes 'x86info -r' dump hypervisor leaf cpu ids
> > (for kvm this is signature+features) when running in a vm.
> > 
> > On the guest we see the signature and the features:
> > eax in: 0x40000000, eax = 00000000 ebx = 4b4d564b ecx = 564b4d56 edx = 
> > 0000004d
> > eax in: 0x40000001, eax = 0100007b ebx = 00000000 ecx = 00000000 edx = 
> > 00000000
> > 
> > Hypervisor flag is checked to avoid output changes when not
> > running on a VM.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > 
> > Changes from v1:
> >     Make work on non KVM hypervisors (only KVM was tested).
> >     Avi Kivity said kvm will in the future report
> >     max HV leaf in eax. For now it reports eax = 0
> >         so add a work around for that.
> > 
> > ---
> > 
> > diff --git a/identify.c b/identify.c
> > index 33f35de..a4a3763 100644
> > --- a/identify.c
> > +++ b/identify.c
> > @@ -9,8 +9,8 @@
> >  
> >  void get_cpu_info_basics(struct cpudata *cpu)
> >  {
> > -   unsigned int maxi, maxei, vendor, address_bits;
> > -   unsigned int eax;
> > +   unsigned int maxi, maxei, maxhv, vendor, address_bits;
> > +   unsigned int eax, ebx, ecx;
> >  
> >     cpuid(cpu->number, 0, &maxi, &vendor, NULL, NULL);
> >     maxi &= 0xffff;         /* The high-order word is non-zero on some 
> > Cyrix CPUs */
> > @@ -19,7 +19,7 @@ void get_cpu_info_basics(struct cpudata *cpu)
> >             return;
> >  
> >     /* Everything that supports cpuid supports these. */
> > -   cpuid(cpu->number, 1, &eax, NULL, NULL, NULL);
> > +   cpuid(cpu->number, 1, &eax, &ebx, &ecx, NULL);
> 
> You probably want to check ebx, ecx, edx for the signatures of the
> hypervisor's you are willing to support and which you know do something
> sane with eax? Also it would be something worth reporting in its own
> right?
> 
Yes, but this is for -r option which only dumps raw cpuid info.
Decoding hypervisor specific info is useful thing, but should not be
pre-request for that patch.

> 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?

> 
> Ian.
> 
> > +            * Most (all?) hypervisors have at least one CPUID besides
> > +            * the vendor ID so assume that.
> > +            */
> > +           cpu->maxhv = maxhv ? maxhv : 0x40000001;
> > +   } else {
> > +           /* Suppress hypervisor cpuid unless running on a hypervisor */
> > +           cpu->maxhv = 0;
> > +   }
> >  
> >     cpuid(cpu->number, 0x80000008,&address_bits, NULL, NULL, NULL);
> >     cpu->phyaddr_bits = address_bits & 0xFF;
> > diff --git a/x86info.c b/x86info.c
> > index 22c4734..80cae36 100644
> > --- a/x86info.c
> > +++ b/x86info.c
> > @@ -44,6 +44,10 @@ static void display_detailed_info(struct cpudata *cpu)
> >  
> >             if (cpu->maxei2 >=0xC0000000)
> >                     dump_raw_cpuid(cpu->number, 0xC0000000, cpu->maxei2);
> > +
> > +           if (cpu->maxhv >= 0x40000000)
> > +                   dump_raw_cpuid(cpu->number, 0x40000000, cpu->maxhv);
> > +
> >     }
> >  
> >     if (show_cacheinfo) {
> > diff --git a/x86info.h b/x86info.h
> > index 7d2a455..c4f5d81 100644
> > --- a/x86info.h
> > +++ b/x86info.h
> > @@ -84,7 +84,7 @@ struct cpudata {
> >     unsigned int cachesize_trace;
> >     unsigned int phyaddr_bits;
> >     unsigned int viraddr_bits;
> > -   unsigned int cpuid_level, maxei, maxei2;
> > +   unsigned int cpuid_level, maxei, maxei2, maxhv;
> >     char name[CPU_NAME_LEN];
> >     enum connector connector;
> >     unsigned int flags_ecx;
> > _______________________________________________
> > Virtualization mailing list
> > Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > https://lists.linuxfoundation.org/mailman/listinfo/virtualization
> > 
> 
> -- 
> Ian Campbell
> 
> Your own qualities will help prevent your advancement in the world.
> 
> --
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--
                        Gleb.

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