Re: [PATCH v2 2/4] KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN

[Paolo Bonzini]

On 1/17/22 16:05, Vitaly Kuznetsov wrote:
>   
> +/* Check whether the supplied CPUID data is equal to what is already set for the vCPU. */
> +static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
> +				 int nent)
> +{
> +	struct kvm_cpuid_entry2 *best;
> +	int i;
> +
> +	for (i = 0; i < nent; i++) {
> +		best = kvm_find_cpuid_entry(vcpu, e2[i].function, e2[i].index);
> +		if (!best)
> +			return -EINVAL;
> +
> +		if (e2[i].eax != best->eax || e2[i].ebx != best->ebx ||
> +		    e2[i].ecx != best->ecx || e2[i].edx != best->edx)
> +			return -EINVAL;
> +	}
> +
> +	return 0;
> +}

What about this alternative implementation:

/* Check whether the supplied CPUID data is equal to what is already set for the vCPU. */
static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
                                 int nent)
{
        struct kvm_cpuid_entry2 *orig;
        int i;

        if (nent != vcpu->arch.cpuid_nent)
                return -EINVAL;

        for (i = 0; i < nent; i++) {
                orig = &vcpu->arch.cpuid_entries[i];
                if (e2[i].function != orig->function ||
                    e2[i].index != orig->index ||
                    e2[i].eax != orig->eax || e2[i].ebx != orig->ebx ||
                    e2[i].ecx != orig->ecx || e2[i].edx != orig->edx)
                        return -EINVAL;
        }

        return 0;
}

avoiding the repeated calls to kvm_find_cpuid_entry?

Paolo