On Thu, Mar 09, 2017 at 05:13:33PM +0100, Paolo Bonzini wrote:
> This is not how you check if running under a hypervisor; you should
> check the HYPERVISOR bit, i.e. bit 31 of cpuid(1).ecx. This in turn
> tells you if leaf 0x40000000 is valid.
Ah, good point, I already do that in the microcode loader :)
/*
* CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
* completely accurate as xen pv guests don't see that CPUID bit set but
* that's good enough as they don't land on the BSP path anyway.
*/
if (native_cpuid_ecx(1) & BIT(31))
return *res;
> That said, the main issue with this function is that it hardcodes the
> behavior for KVM. It is possible that another hypervisor defines its
> 0x40000001 leaf in such a way that KVM_FEATURE_SEV has a different meaning.
>
> Instead, AMD should define a "well-known" bit in its own space (i.e.
> 0x800000xx) that is only used by hypervisors that support SEV. This is
> similar to how Intel defined one bit in leaf 1 to say "is leaf
> 0x40000000 valid".
>
> > + if (eax > 0x40000000) {
> > + eax = 0x40000001;
> > + ecx = 0;
> > + native_cpuid(&eax, &ebx, &ecx, &edx);
> > + if (!(eax & BIT(KVM_FEATURE_SEV)))
> > + goto out;
> > +
> > + eax = 0x8000001f;
> > + ecx = 0;
> > + native_cpuid(&eax, &ebx, &ecx, &edx);
> > + if (!(eax & 1))
Right, so this is testing CPUID_0x8000001f_ECX(0)[0], SME. Why not
simply set that bit for the guest too, in kvm?
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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