linux-kernel - Re: [PATCH] x86/cpufeature: Document cpu_feature

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Message-ID: <f9cd603d-8a3f-43fc-a670-75b4d9a6c729@intel.com>
Date: Thu, 31 Oct 2024 11:26:27 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Borislav Petkov <bp@...en8.de>
CC: Yazen Ghannam <yazen.ghannam@....com>, "Luck, Tony" <tony.luck@...el.com>,
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Subject: Re: [PATCH] x86/cpufeature: Document cpu_feature_enabled() as the
 default to use

On 10/31/2024 3:34 AM, Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@...en8.de>
> 
> cpu_feature_enabled() should be used in most cases when CPU feature
> support needs to be tested in code. Document that.
> 
> Reported-by: Sohil Mehta <sohil.mehta@...el.com>
> Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
> ---
>  arch/x86/include/asm/cpufeature.h | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
> 

Looks good (a minor nit below),
Reviewed-by: Sohil Mehta <sohil.mehta@...el.com>


> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index 0b9611da6c53..de1ad09fe8d7 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -132,11 +132,12 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>  	 x86_this_cpu_test_bit(bit, cpu_info.x86_capability))
>  
>  /*
> - * This macro is for detection of features which need kernel
> - * infrastructure to be used.  It may *not* directly test the CPU
> - * itself.  Use the cpu_has() family if you want true runtime
> - * testing of CPU features, like in hypervisor code where you are
> - * supporting a possible guest feature where host support for it
> + * This is the default CPU features testing macro to use in code.
> + *

Does "default CPU feature testing macro" roll better than "default CPU
features testing macro"?

> + * It is for detection of features which need kernel infrastructure to be
> + * used.  It may *not* directly test the CPU itself.  Use the cpu_has() family
> + * if you want true runtime testing of CPU features, like in hypervisor code
> + * where you are supporting a possible guest feature where host support for it
>   * is not relevant.
>   */