Re: [PATCH v3 8/9] KVM: nSVM: Advertise DecodeAssists to L1

On 7/30/2026 8:33 PM, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] Missing VENDOR_F(DECODEASSISTS) initialization in CPUID 0x8000000A leaf definition.
> --
> 
> --- Patch [8]: [PATCH v3 8/9] KVM: nSVM: Advertise DecodeAssists to L1 ---
> commit 2694559bd05c1133d7f21075f9c95dc19418651a
> Author: Tina Zhang <[email protected]>
> 
> KVM: nSVM: Advertise DecodeAssists to L1
> 
> This patch advertises DecodeAssists to L1 guests by checking and setting
> the X86_FEATURE_DECODEASSISTS capability when supported by hardware. This
> enables QEMU configurations that enforce the decodeassists feature.
> 
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index 6e2ceb700567c..4e01a6ede4246 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -5588,6 +5588,8 @@ static __init void svm_set_cpu_caps(void)
>>   		 */
>>   		kvm_cpu_cap_set(X86_FEATURE_FLUSHBYASID);
>>   
>> +		kvm_cpu_cap_check_and_set(X86_FEATURE_DECODEASSISTS);
> 
> [Severity: Low]
> Does this feature also need to be initialized in arch/x86/kvm/cpuid.c?
> 
> Currently, kvm_cpu_cap_check_and_set() is used here to enable it, but
> VENDOR_F(DECODEASSISTS) appears to be missing from the CPUID_8000_000A_EDX
> capabilities array in cpuid.c:
> 
> arch/x86/kvm/cpuid.c:kvm_cpu_cap_init() {
>      /* All SVM features required additional vendor module enabling. */
>      kvm_cpu_cap_init(CPUID_8000_000A_EDX,
>          VENDOR_F(NPT),
>          VENDOR_F(VMCBCLEAN),
>          ...
> }
> 
> Without VENDOR_F(DECODEASSISTS), this skips KVM's standard compile-time
> validation and raw CPUID masking logic. Should it be added to the vendor
> feature list as well?

Yes, DecodeAssists should also be declared with VENDOR_F(DECODEASSISTS).
I'll add it in the next version.

Thanks,
Tina
> 
>> +
>>   		if (nrips)
>>   			kvm_cpu_cap_set(X86_FEATURE_NRIPS);
>>
>