Re: [PATCH v2 1/2] x86/cpu: Refactor RFDS mitigation to use X86_FEATURE_RFDS_CLEAR

[Borislav Petkov <bp@alien8.de>]

On Fri, Jan 30, 2026 at 09:33:39PM +0900, Joongsun Moon-Lee wrote:
> The current RFDS mitigation logic relies on verw_clears_cpu_reg_file(),
> which directly checks the RFDS_CLEAR bit in the IA32_ARCH_CAPABILITIES MSR.
> 
> To support quirks for CPUs that mitigate RFDS but do not enumerate it,
> transition to using the synthetic feature flag X86_FEATURE_RFDS_CLEAR.
> 
> Replace the MSR-bit-based check with boot_cpu_has(X86_FEATURE_RFDS_CLEAR)
> and synthesize this feature bit in rfds_select_mitigation() if the
> architectural RFDS_CLEAR bit is present.

Please do not explain the diff - talk about why this patch exists and other
details which are not obvious from the code.

> @@ -670,7 +665,10 @@ static void __init rfds_select_mitigation(void)
>  	if (rfds_mitigation == RFDS_MITIGATION_OFF)
>  		return;
>  
> -	if (verw_clears_cpu_reg_file())
> +	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
> +		setup_force_cpu_cap(X86_FEATURE_RFDS_CLEAR);
> +
> +	if (boot_cpu_has(X86_FEATURE_RFDS_CLEAR))
>  		verw_clear_cpu_buf_mitigation_selected = true;
>  }

So:
	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR) {
		setup_force_cpu_cap(X86_FEATURE_RFDS_CLEAR);
		verw_clear_cpu_buf_mitigation_selected = true;
	}

?

-- 
Regards/Gruss,
    Boris.

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