linux-kernel - Re: [PATCH v2 18/49] KVM: x86: Account for max supported CPUID leaf when getting raw host CPUID

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Message-ID: <cb6e3c03-547b-4223-8dd4-3bc2e4fd4dff@intel.com>
Date: Wed, 19 Jun 2024 14:17:31 +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 18/49] KVM: x86: Account for max supported CPUID leaf
 when getting raw host CPUID

On 5/18/2024 1:38 AM, Sean Christopherson wrote:

[...]

>   /* Mask kvm_cpu_caps for @leaf with the raw CPUID capabilities of this CPU. */
>   static __always_inline void __kvm_cpu_cap_mask(unsigned int leaf)
>   {
>   	const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32);
> -	struct kvm_cpuid_entry2 entry;
>   
>   	reverse_cpuid_check(leaf);

IIUC, this reverse_cpuid_check() is redundant since it's already enforced in x86_feature_cpuid() via __feature_leaf() as previous patch(17) shows.
>   
> -	cpuid_count(cpuid.function, cpuid.index,
> -		    &entry.eax, &entry.ebx, &entry.ecx, &entry.edx);
> -
> -	kvm_cpu_caps[leaf] &= *__cpuid_entry_get_reg(&entry, cpuid.reg);
> +	kvm_cpu_caps[leaf] &= raw_cpuid_get(cpuid);
>   }
>   
>   static __always_inline