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

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Message-ID: <c427371c-474e-1233-4e57-66210bfc5687@redhat.com>
Date:   Mon, 17 Jan 2022 18:30:07 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] KVM: x86: Partially allow KVM_SET_CPUID{,2} after
 KVM_RUN

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