Re: [PATCH 21/25] KVM: x86: Introduce KVM_TDX_GET_CPUID

Paolo Bonzini
2024-09-10T17:29:18Z

On 9/3/24 09:19, Tony Lindgren wrote:
>>> + gpa_t gpa_bits = gfn_to_gpa(kvm_gfn_direct_bits(vcpu->kvm));
>>> + unsigned int g_maxpa = __ffs(gpa_bits) + 1;
>>> +
>>> + output_e->eax &= ~0x00ff0000;
>>> + output_e->eax |= g_maxpa << 16;
>> Is it possible this workaround escapes the KVM supported bits check?
>
> Yes it might need a mask for (g_maxpa << 16) & 0x00ff0000 to avoid setting
> the wrong bits, will check.

The mask is okay, __ffs(gpa_bits) + 1 will be between 1 and 64.

The question is whether the TDX module will accept nonzero bits 16..23
of CPUID[0x80000008].EAX.

Paolo