Re: [PATCH 6/6] KVM: x86: Mask off reserved bits in CPUID.8000001FH

[Paolo Bonzini <pbonzini@redhat.com>]

On 9/30/22 00:52, Jim Mattson wrote:
> KVM_GET_SUPPORTED_CPUID should only enumerate features that KVM
> actually supports. CPUID.8000001FH:EBX[31:16] are reserved bits and
> should be masked off.
> 
> Fixes: 8765d75329a3 ("KVM: X86: Extend CPUID range to include new leaf")
> Signed-off-by: Jim Mattson <jmattson@google.com>
> ---
>   arch/x86/kvm/cpuid.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 576cbcf489ce..58dabc9e54db 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -1188,7 +1188,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>   			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
>   		} else {
>   			cpuid_entry_override(entry, CPUID_8000_001F_EAX);
> -
> +			entry->ebx &= ~GENMASK(31, 16);
>   			/*
>   			 * Enumerate '0' for "PA bits reduction", the adjusted
>   			 * MAXPHYADDR is enumerated directly (see 0x80000008).

I think 15:12 (number of VMPLs supported) should also be masked off 
since KVM does not support SEV-SNP.

Paolo