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?
Everyone puts the max leaf in eax - this is what hardware
CPUs do. So I think we can just interpret eax as such.
If someone wants to put broken info in cpuid,
send a patch to blacklist it.
> Also it would be something worth reporting in its own
> right?
>
> 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.
>
> Ian.
kvm lets users change the signature.
But worst case we print one useless line.
Better than not printing something potentially useful.
--
MST
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