Re: [PATCH v3 4/9] KVM: x86: Extend CPUID range to include new leaf

[Jim Mattson <jmattson@google.com>]

On Tue, Mar 10, 2026 at 06:00:16AM +0000, Manali Shukla wrote:
> CPUID leaf 0x8000001b (EAX) provides information about Instruction-Based
> sampling capabilities on AMD Platforms. Add the new leaf to
> kvm_cpu_cap_init() using F() macros, which automatically gate each
> capability bits against raw hardware CPUID via raw_cpuid_get().
>
> This allows vendor code to simply clear entire leaf when vibs is not
> enabled, rather than reading hardware CPUID and calling
> kvm_cpu_cap_set() for each capability bits inidividually in later
> patches.
>
> Signed-off-by: Manali Shukla <manali.shukla@amd.com>

The shortlog is not accurate. The CPUID range does not change; case
0x80000000 already limits the maximum extended leaf to 0x80000022, which
includes 0x8000001B. Before this patch, leaf 0x8000001B went to the default
case, which returns all zeros. This patch adds KVM's supported bits for the
leaf and a case that reports them when X86_FEATURE_IBS is supported. Please
change the shortlog to say that.

Also, there are some typos in the changelog:
  - "Instruction-Based sampling" should be "Instruction-Based Sampling"
  - "capability bits" should be "capability bit" (twice)
  - "inidividually" should be "individually"
  - "vibs" should be "VIBS"

> ---
>  arch/x86/kvm/cpuid.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 96a08a556543..4e626e77e6a6 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c

[...]

> @@ -1848,6 +1864,15 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		entry->eax = entry->ebx = entry->ecx = 0;
>  		entry->edx = 0; /* reserved */
>  		break;
> +	/* AMD IBS capability */
> +	case 0x8000001B:
> +		if (!kvm_cpu_cap_has(X86_FEATURE_IBS))
> +			entry->eax = 0;
> +		else
> +			cpuid_entry_override(entry, CPUID_8000_001B_EAX);
> +
> +		entry->ebx = entry->ecx = entry->edx = 0;
> +		break;

Please put case 0x8000001b between case 0x8000001a and case 0x8000001e.

>  	case 0x8000001F:
>  		if (!kvm_cpu_cap_has(X86_FEATURE_SEV)) {
>  			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;