Re: [PATCH v5 17/20] KVM: x86: Expose APX foundation feature to userspace

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] CPUID leaf 0x29 is not added to cpuid_function_is_indexed(), preventing KVM from properly flagging it as a multi-subleaf CPUID.
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--- Patch [17]: [PATCH v5 17/20] KVM: x86: Expose APX foundation feature to userspace ---
commit e317b8613a3aae9996b941415cb6b3fe55b0643f
Author: Chang S. Bae <chang.seok.bae@intel.com>

KVM: x86: Expose APX foundation feature to userspace

This commit exposes the APX feature to userspace components and updates the
maximum supported CPUID leaf to 0x29. It clears the APX feature on SVM
environments since EGPR support is not yet implemented.

> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
[ ... ]
> @@ -1713,6 +1717,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		}
>  		break;
>  	}
> +	/* APX sub-features */
> +	case 0x29:
> +		entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> +		break;

[Severity: Medium]
Should CPUID leaf 0x29 also be added to cpuid_function_is_indexed() in
arch/x86/include/asm/cpuid/api.h?

Without adding it there, KVM will not set KVM_CPUID_FLAG_SIGNIFCANT_INDEX
for leaf 0x29. This causes kvm_find_cpuid_entry2() to ignore the
guest-provided ECX sub-leaf index when resolving this leaf.

If a VMM populates leaf 0x29 index 0 with APX features, a guest querying
index 1 will incorrectly receive the features of index 0 instead of
all-zeros.

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Sashiko AI review · https://sashiko.dev/#/patchset/20260720171949.498680-1-chang.seok.bae@intel.com?part=17