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Subject: Re: [PATCH 1/5] x86/cpufeatures: Define feature bits to support
 mitigation of PSF
To:     Borislav Petkov <bp@alien8.de>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>
References: <20210406155004.230790-1-rsaripal@amd.com>
 <20210406155004.230790-2-rsaripal@amd.com> <20210409174134.GH15567@zn.tnic>
From:   "Saripalli, RK" <rsaripal@amd.com>
Message-ID: <cc5476c9-fe4e-6b4c-d323-37b90237b32b@amd.com>
Date:   Fri, 9 Apr 2021 13:22:49 -0500
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On 4/9/2021 12:41 PM, Borislav Petkov wrote:
> 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...

Boris, I added this bit so we could detect later that PSF is supported.
But since PSF is AMD specific for now, I guess I will go along with your suggestions.
> 
>>  #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 "".
Ok
> 
>>  
>>  /* 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.
> 
Ok.
> Thx.
>