Re: [PATCH v8 08/26] KVM: x86: Rework cpuid_get_supported_xcr0() to operate on vCPU data

[Maxim Levitsky]

On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> 
> Rework and rename cpuid_get_supported_xcr0() to explicitly operate on
> vCPU state, i.e. on a vCPU's CPUID state, now that the only usage of
> the helper is to retrieve a vCPU's already-set CPUID.
> 
> Prior to commit 275a87244ec8 ("KVM: x86: Don't adjust guest's CPUID.0x12.1
> (allowed SGX enclave XFRM)"), KVM incorrectly fudged guest CPUID at runtime,
> which in turn necessitated massaging the incoming CPUID state for
> KVM_SET_CPUID{2} so as not to run afoul of kvm_cpuid_check_equal().
> I.e. KVM also invoked cpuid_get_supported_xcr0() with the incoming CPUID
> state, and thus without an explicit vCPU object.
> 
> Opportunistically move the helper below kvm_update_cpuid_runtime() to make
> it harder to repeat the mistake of querying supported XCR0 for runtime
> updates.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
>  arch/x86/kvm/cpuid.c | 33 ++++++++++++++++-----------------
>  1 file changed, 16 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 294e5bd5f8a0..624954203b40 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -247,21 +247,6 @@ void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)
>  		vcpu->arch.pv_cpuid.features = best->eax;
>  }
>  
> -/*
> - * Calculate guest's supported XCR0 taking into account guest CPUID data and
> - * KVM's supported XCR0 (comprised of host's XCR0 and KVM_SUPPORTED_XCR0).
> - */
> -static u64 cpuid_get_supported_xcr0(struct kvm_cpuid_entry2 *entries, int nent)
> -{
> -	struct kvm_cpuid_entry2 *best;
> -
> -	best = cpuid_entry2_find(entries, nent, 0xd, 0);
> -	if (!best)
> -		return 0;
> -
> -	return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
> -}
> -
>  static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *entries,
>  				       int nent)
>  {
> @@ -312,6 +297,21 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
>  }
>  EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);
>  
> +/*
> + * Calculate guest's supported XCR0 taking into account guest CPUID data and
> + * KVM's supported XCR0 (comprised of host's XCR0 and KVM_SUPPORTED_XCR0).
> + */
> +static u64 vcpu_get_supported_xcr0(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_cpuid_entry2 *best;
> +
> +	best = kvm_find_cpuid_entry_index(vcpu, 0xd, 0);
> +	if (!best)
> +		return 0;
> +
> +	return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
> +}
> +
>  static bool kvm_cpuid_has_hyperv(struct kvm_cpuid_entry2 *entries, int nent)
>  {
>  #ifdef CONFIG_KVM_HYPERV
> @@ -361,8 +361,7 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>  		kvm_apic_set_version(vcpu);
>  	}
>  
> -	vcpu->arch.guest_supported_xcr0 =
> -		cpuid_get_supported_xcr0(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent);
> +	vcpu->arch.guest_supported_xcr0 = vcpu_get_supported_xcr0(vcpu);
>  
>  	kvm_update_pv_runtime(vcpu);
>  

Looks like I forgot to add my reviewed-by:

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky