Re: [PATCH v10 2/3] x86/cpu: Check if feature string is non-zero

[Maciej Wieczor-Retman]

On 2026-03-18 at 16:41:58 -0700, Pawan Gupta wrote:
>On Tue, Mar 17, 2026 at 08:00:16PM +0000, Maciej Wieczor-Retman wrote:
>> From: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
>> 
>> In filter_cpuid_features(), x86_cap_flags[] is read, but it's not verified
>> whether the string is non-zero which could lead to unwanted output.
>> 
>> In two more places there are open coded paths that try to retrieve a
>> feature string, and if there isn't one, the feature word and bit are
>> returned instead.
>> 
>> Add a common helper to fix filter_cpuid_features() as well as clean up
>> the open coded cases.
>> 
>> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
>> ---
>> Changelog v10:
>> - Reword the patch message a bit.
>> - Move x86_cap_name() declaration and X86_CAP_BUF_SIZE define to
>>   asm/cpufeature.h.
>> - Don't include asm/cpu.h in cpuid-deps.c
>> - Extend the comment above x86_cap_name to include information on buffer
>>   size that needs to be prepared before calling the function.
>> - Remove the likely(), unlikely() calls since this is not a hot path.
>> 
>> Changelog v9:
>> - 16 -> X86_CAP_BUF_SIZE.
>> - Add comment to the x86_cap_name().
>> 
>> Changelog v8:
>> - Move x86_cap_name() declaration from linux/cpu.h to the arch/cpu.h.
>>   Include arch/cpu.h in the cpuid-deps.c file instead of linux/cpu.h.
>> 
>> Changelog v7:
>> - sizeof(buf) -> 16
>> - Rebase onto 7.01-rc1.
>> 
>> Changelog v6:
>> - Remove parts of the patch message that are redundant and just copy
>>   what's visible in the diff.
>> - Redo the helper to use an external char buffer instead of a local
>>   static string.
>> 
>>  arch/x86/include/asm/cpufeature.h |  4 ++++
>>  arch/x86/kernel/cpu/common.c      | 32 ++++++++++++++++++++++++++-----
>>  arch/x86/kernel/cpu/cpuid-deps.c  | 21 +++-----------------
>>  3 files changed, 34 insertions(+), 23 deletions(-)
>> 
>> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
>> index 3ddc1d33399b..dc1cd44ddd63 100644
>> --- a/arch/x86/include/asm/cpufeature.h
>> +++ b/arch/x86/include/asm/cpufeature.h
>> @@ -138,5 +138,9 @@ static __always_inline bool _static_cpu_has(u16 bit)
>>  #define CPU_FEATURE_TYPEVAL		boot_cpu_data.x86_vendor, boot_cpu_data.x86, \
>>  					boot_cpu_data.x86_model
>>  
>> +#define X86_CAP_BUF_SIZE			16
>
>This can get rid of the extra tab.
>
>Reviewed-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>

Thanks, I'll delete that extra tab.

-- 
Kind regards
Maciej Wieczór-Retman