linux-kernel - Re: [PATCH 1/5] x86/cpufeatures: Define feature bits to support mitigation of PSF

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Date:   Fri, 9 Apr 2021 19:41:34 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ramakrishna Saripalli <rsaripal@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 1/5] x86/cpufeatures: Define feature bits to support
 mitigation of PSF

On Tue, Apr 06, 2021 at 10:50:00AM -0500, Ramakrishna Saripalli wrote:
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index cc96e26d69f7..21e7f8d0d7d9 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -201,7 +201,7 @@
>  #define X86_FEATURE_INVPCID_SINGLE	( 7*32+ 7) /* Effectively INVPCID && CR4.PCIDE=1 */
>  #define X86_FEATURE_HW_PSTATE		( 7*32+ 8) /* AMD HW-PState */
>  #define X86_FEATURE_PROC_FEEDBACK	( 7*32+ 9) /* AMD ProcFeedbackInterface */
> -/* FREE!                                ( 7*32+10) */
> +#define X86_FEATURE_PSFD		( 7*32+10) /* Predictive Store Forward Disable */

You don't need this one...

>  #define X86_FEATURE_PTI			( 7*32+11) /* Kernel Page Table Isolation enabled */
>  #define X86_FEATURE_RETPOLINE		( 7*32+12) /* "" Generic Retpoline mitigation for Spectre variant 2 */
>  #define X86_FEATURE_RETPOLINE_AMD	( 7*32+13) /* "" AMD Retpoline mitigation for Spectre variant 2 */
> @@ -309,6 +309,7 @@
>  #define X86_FEATURE_AMD_SSBD		(13*32+24) /* "" Speculative Store Bypass Disable */
>  #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* Virtualized Speculative Store Bypass Disable */
>  #define X86_FEATURE_AMD_SSB_NO		(13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
> +#define X86_FEATURE_AMD_PSFD		(13*32+28) /* "" Predictive Store Forward Disable */

... when you have this one. And this one is AMD-specific so you can just
as well call it X86_FEATURE_PSFD and remove the "".

>  
>  /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
>  #define X86_FEATURE_DTHERM		(14*32+ 0) /* Digital Thermal Sensor */
> @@ -428,5 +429,6 @@
>  #define X86_BUG_TAA			X86_BUG(22) /* CPU is affected by TSX Async Abort(TAA) */
>  #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* CPU may incur MCE during certain page attribute changes */
>  #define X86_BUG_SRBDS			X86_BUG(24) /* CPU may leak RNG bits if not mitigated */
> +#define X86_BUG_PSF			X86_BUG(25) /* CPU is affected by Predictive Store Forwarding attack */

And I think you don't need this one either if we do a "light" controls
thing but lemme look at the rest first.

Thx.

-- 
Regards/Gruss,
    Boris.

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