On Sat, Oct 22, 2022, Paolo Bonzini wrote:
> Several fields of CPUID.8000001EH (ExtendedApicId in EAX[31:0],
> CoreId in EBX[7:0], NodeId in ECX[7:0]) vary on each processor,
> and it is simply impossible to fit the right values in the
> KVM_GET_SUPPORTED_CPUID API, in such a way that they can be
> passed to KVM_SET_CPUID2.
The same is true for 0xb and 0x1f, why delete 0x8000001e but keep those? I agree
that KVM_GET_SUPPORTED_CPUID can't get this right, but KVM can at least be
consistent with itself.
> The most likely way to avoid confusion in the guest is to zero
> out all the values. Userspace will most likely override it
> anyway if it want to present a specific topology to the guest.
>
> This patch essentially reverts commit 382409b4c43e ("kvm: x86: Include
> CPUID leaf 0x8000001e in kvm's supported CPUID").
Why not do a full revert?
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/cpuid.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index a0292ba650df..380b71600a9e 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -1193,6 +1193,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> entry->ebx = entry->ecx = entry->edx = 0;
> break;
> case 0x8000001e:
> + /* Different on each processor, just hide it. */
> + entry->eax = entry->ebx = entry->ecx = 0;
> + entry->edx = 0;
Putting EDX in a separate line is rather weird.
