Re: [PATCH v2 01/66] KVM: x86: Return -E2BIG when KVM_GET_SUPPORTED_CPUID hits max entries

Paolo Bonzini
2020-03-03T14:16:25Z

On 03/03/20 00:56, Sean Christopherson wrote:
> (KVM hard caps CPUID 0xD at a single sub-leaf).

Hmm... no it doesn't?

for (idx = 1, i = 1; idx < 64; ++idx) {
u64 mask = ((u64)1 << idx);
if (*nent >= maxnent)
goto out;

do_host_cpuid(&entry[i], function, idx);
if (idx == 1) {
entry[i].eax &= kvm_cpuid_D_1_eax_x86_features;
cpuid_mask(&entry[i].eax, CPUID_D_1_EAX);
entry[i].ebx = 0;
if (entry[i].eax & (F(XSAVES)|F(XSAVEC)))
entry[i].ebx =
xstate_required_size(supported,
true);
} else {
if (entry[i].eax == 0 || !(supported & mask))
continue;
if (WARN_ON_ONCE(entry[i].ecx & 1))
continue;
}
entry[i].ecx = 0;
entry[i].edx = 0;
++*nent;
++i;
}

I still think the patch is correct, what matters is that no KVM in
existence supports enough processor features to reach 100 or so subleaves.

Paolo