Re: [PATCH 10/11] x86/fpu: Remove unnecessary CPUID level check

Sean Christopherson
2024-11-21T15:45:19Z

On Wed, Nov 20, 2024, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> The CPUID level dependency table will entirely zap X86_FEATURE_XSAVE

What table is that? XSAVE depends on FXSR, but I can't find anything that clears
X86_FEATURE_XSAVE if cpuid_level < XSTATE_CPUID. Even if it did, dropping a
sanity check in a one-time path adds risk for almost no reward.

> if the CPUID level is too low. This code is unreachable. Kill it.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> ---
>
> b/arch/x86/kernel/fpu/xstate.c | 5 -----
> 1 file changed, 5 deletions(-)
>
> diff -puN arch/x86/kernel/fpu/xstate.c~xsave-leaf-checks-2 arch/x86/kernel/fpu/xstate.c
> --- a/arch/x86/kernel/fpu/xstate.c~xsave-leaf-checks-2 2024-11-20 11:44:20.369771244 -0800
> +++ b/arch/x86/kernel/fpu/xstate.c 2024-11-20 11:44:20.373771397 -0800
> @@ -764,11 +764,6 @@ void __init fpu__init_system_xstate(unsi
> return;
> }
>
> - if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
> - WARN_ON_FPU(1);
> - return;
> - }
> -
> /*
> * Find user xstates supported by the processor.
> */
> _