linux-kernel - Re: [PATCH v2 17/49] KVM: x86: Do reverse CPUID sanity checks in __feature

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Message-ID: <e24729812e915b4d195ec0259a6dfa0c4c6d5be8.camel@redhat.com>
Date: Thu, 04 Jul 2024 21:17:51 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>,  Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: 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>, Binbin Wu <binbin.wu@...ux.intel.com>, Yang
 Weijiang <weijiang.yang@...el.com>, Robert Hoo <robert.hoo.linux@...il.com>
Subject: Re: [PATCH v2 17/49] KVM: x86: Do reverse CPUID sanity checks in
 __feature_leaf()

On Fri, 2024-05-17 at 10:38 -0700, Sean Christopherson wrote:
> Do the compile-time sanity checks on reverse_cpuid in __feature_leaf() so
> that higher level APIs don't need to "manually" perform the sanity checks.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/cpuid.h         | 3 ---
>  arch/x86/kvm/reverse_cpuid.h | 6 ++++--
>  2 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 7eb3d7318fc4..d68b7d879820 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -198,7 +198,6 @@ static __always_inline void kvm_cpu_cap_clear(unsigned int x86_feature)
>  {
>  	unsigned int x86_leaf = __feature_leaf(x86_feature);
>  
> -	reverse_cpuid_check(x86_leaf);
>  	kvm_cpu_caps[x86_leaf] &= ~__feature_bit(x86_feature);
>  }
>  
> @@ -206,7 +205,6 @@ static __always_inline void kvm_cpu_cap_set(unsigned int x86_feature)
>  {
>  	unsigned int x86_leaf = __feature_leaf(x86_feature);
>  
> -	reverse_cpuid_check(x86_leaf);
>  	kvm_cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
>  }
>  
> @@ -214,7 +212,6 @@ static __always_inline u32 kvm_cpu_cap_get(unsigned int x86_feature)
>  {
>  	unsigned int x86_leaf = __feature_leaf(x86_feature);
>  
> -	reverse_cpuid_check(x86_leaf);
>  	return kvm_cpu_caps[x86_leaf] & __feature_bit(x86_feature);
>  }
>  
> diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
> index 2f4e155080ba..245f71c16272 100644
> --- a/arch/x86/kvm/reverse_cpuid.h
> +++ b/arch/x86/kvm/reverse_cpuid.h
> @@ -136,7 +136,10 @@ static __always_inline u32 __feature_translate(int x86_feature)
>  
>  static __always_inline u32 __feature_leaf(int x86_feature)
>  {
> -	return __feature_translate(x86_feature) / 32;
> +	u32 x86_leaf = __feature_translate(x86_feature) / 32;
> +
> +	reverse_cpuid_check(x86_leaf);
> +	return x86_leaf;
>  }
>  
>  /*
> @@ -159,7 +162,6 @@ static __always_inline struct cpuid_reg x86_feature_cpuid(unsigned int x86_featu
>  {
>  	unsigned int x86_leaf = __feature_leaf(x86_feature);
>  
> -	reverse_cpuid_check(x86_leaf);
>  	return reverse_cpuid[x86_leaf];
>  }
>  

Makes sense.

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky