linux-kernel - Re: [PATCH v2 37/49] KVM: x86: Replace guts of "governed" features with comprehensive cpu

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Date: Thu, 20 Jun 2024 10:20:35 +0800
From: "Yang, Weijiang" <weijiang.yang@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Vitaly Kuznetsov <vkuznets@...hat.com>, Paolo Bonzini
	<pbonzini@...hat.com>, <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Hou Wenlong <houwenlong.hwl@...group.com>, Kechen Lu <kechenl@...dia.com>,
	Oliver Upton <oliver.upton@...ux.dev>, Maxim Levitsky <mlevitsk@...hat.com>,
	Binbin Wu <binbin.wu@...ux.intel.com>, Robert Hoo
	<robert.hoo.linux@...il.com>
Subject: Re: [PATCH v2 37/49] KVM: x86: Replace guts of "governed" features
 with comprehensive cpu_caps

On 5/18/2024 1:39 AM, Sean Christopherson wrote:

[...]

> index e021681f34ac..ad0168d3aec5 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -259,10 +259,10 @@ static __always_inline bool kvm_is_governed_feature(unsigned int x86_feature)
>   static __always_inline void guest_cpu_cap_set(struct kvm_vcpu *vcpu,
>   					      unsigned int x86_feature)
>   {
> -	BUILD_BUG_ON(!kvm_is_governed_feature(x86_feature));
> +	unsigned int x86_leaf = __feature_leaf(x86_feature);
>   
> -	__set_bit(kvm_governed_feature_index(x86_feature),
> -		  vcpu->arch.governed_features.enabled);
> +	reverse_cpuid_check(x86_leaf);

This reverse_cpuid_check() seems unnecessary since in patch(17), we already have moved it in
  __feature_leaf(). But I don't have full source code to double check it now.

> +	vcpu->arch.cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
>   }
>   
>   static __always_inline void guest_cpu_cap_check_and_set(struct kvm_vcpu *vcpu,
> @@ -275,10 +275,10 @@ static __always_inline void guest_cpu_cap_check_and_set(struct kvm_vcpu *vcpu,
>   static __always_inline bool guest_cpu_cap_has(struct kvm_vcpu *vcpu,
>   					      unsigned int x86_feature)
>   {
> -	BUILD_BUG_ON(!kvm_is_governed_feature(x86_feature));
> +	unsigned int x86_leaf = __feature_leaf(x86_feature);
>   
> -	return test_bit(kvm_governed_feature_index(x86_feature),
> -			vcpu->arch.governed_features.enabled);
> +	reverse_cpuid_check(x86_leaf);

Ditto.

> +	return vcpu->arch.cpu_caps[x86_leaf] & __feature_bit(x86_feature);
>   }
>   
>
[...]