linux-kernel - Re: [PATCH] KVM: x86: expose CPUID 0xC000

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Message-ID: <aJtYlfuBSWhXS3dW@google.com>
Date: Tue, 12 Aug 2025 08:07:01 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Ewan Hai <ewanhai-oc@...oxin.com>
Cc: pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, hpa@...or.com, x86@...nel.org, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, ewanhai@...oxin.com, 
	cobechen@...oxin.com, leoliu@...oxin.com, lyleli@...oxin.com
Subject: Re: [PATCH] KVM: x86: expose CPUID 0xC000_0000 for Zhaoxin "Shanghai" vendor

On Sun, Aug 10, 2025, Ewan Hai wrote:
> rename the local constant CENTAUR_CPUID_SIGNATURE to ZHAOXIN_CPUID_SIGNATURE. 

Why?  I'm not inclined to rename any of the Centaur references, as I don't see
any point in effectively rewriting history.  If we elect to rename things, then
it needs to be done in a separate patch, there needs to be proper justification,
and _all_ references should be converted, e.g. converting just this one macro
creates discrepancies even with cpuid.c, as there are multiple comments that
specifically talk about Centaur CPUID leaves.

> The constant is used only inside cpuid.c, so the rename is NFC outside this
> file.
> 
> Signed-off-by: Ewan Hai <ewanhai-oc@...oxin.com>
> ---
>  arch/x86/kvm/cpuid.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index e2836a255b16..beb83eaa1868 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -1811,7 +1811,7 @@ static int do_cpuid_func(struct kvm_cpuid_array *array, u32 func,
>  	return __do_cpuid_func(array, func);
>  }
>  
> -#define CENTAUR_CPUID_SIGNATURE 0xC0000000
> +#define ZHAOXIN_CPUID_SIGNATURE 0xC0000000
>  
>  static int get_cpuid_func(struct kvm_cpuid_array *array, u32 func,
>  			  unsigned int type)
> @@ -1819,8 +1819,9 @@ static int get_cpuid_func(struct kvm_cpuid_array *array, u32 func,
>  	u32 limit;
>  	int r;
>  
> -	if (func == CENTAUR_CPUID_SIGNATURE &&
> -	    boot_cpu_data.x86_vendor != X86_VENDOR_CENTAUR)
> +	if (func == ZHAOXIN_CPUID_SIGNATURE &&
> +		boot_cpu_data.x86_vendor != X86_VENDOR_CENTAUR &&
> +		boot_cpu_data.x86_vendor != X86_VENDOR_ZHAOXIN)

Align indentation.

	if (func == CENTAUR_CPUID_SIGNATURE &&
	    boot_cpu_data.x86_vendor != X86_VENDOR_CENTAUR &&
	    boot_cpu_data.x86_vendor != X86_VENDOR_ZHAOXIN)
		return 0;

>  		return 0;
>  
>  	r = do_cpuid_func(array, func, type);
> @@ -1869,7 +1870,7 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
>  			    unsigned int type)
>  {
>  	static const u32 funcs[] = {
> -		0, 0x80000000, CENTAUR_CPUID_SIGNATURE, KVM_CPUID_SIGNATURE,
> +		0, 0x80000000, ZHAOXIN_CPUID_SIGNATURE, KVM_CPUID_SIGNATURE,
>  	};
>  
>  	struct kvm_cpuid_array array = {
> -- 
> 2.34.1
>