linux-kernel - Re: [PATCH 2/3] x86/cpu/amd: Add feature bit for MSR_AMD64_LS

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Message-ID: <20221108225141.aikng7veemp25p62@desk>
Date:   Tue, 8 Nov 2022 14:51:41 -0800
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>, hdegoede@...hat.com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        antonio.gomez.iglesias@...ux.intel.com
Subject: Re: [PATCH 2/3] x86/cpu/amd: Add feature bit for MSR_AMD64_LS_CFG
 enumeration

On Tue, Nov 08, 2022 at 07:54:01PM +0100, Borislav Petkov wrote:
>On Mon, Sep 12, 2022 at 04:40:47PM -0700, Pawan Gupta wrote:
>> Currently there is no easy way to enumerate MSR_AMD64_LS_CFG. As this
>> MSR is supported on AMD CPU families 10h to 18h, set a new feature bit
>> on these CPU families. The new bit can be used to detect the MSR
>> support.
>>
>> Suggested-by: Andrew Cooper <andrew.cooper3@...rix.com>
>> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
>> ---
>>  arch/x86/include/asm/cpufeatures.h | 1 +
>>  arch/x86/kernel/cpu/amd.c          | 3 +++
>>  2 files changed, 4 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
>> index dd173733e40d..90bdb1d98531 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -305,6 +305,7 @@
>>  #define X86_FEATURE_USE_IBPB_FW		(11*32+16) /* "" Use IBPB during runtime firmware calls */
>>  #define X86_FEATURE_RSB_VMEXIT_LITE	(11*32+17) /* "" Fill RSB on VM exit when EIBRS is enabled */
>>  #define X86_FEATURE_MSR_TSX_CTRL	(11*32+18) /* "" MSR IA32_TSX_CTRL */
>> +#define X86_FEATURE_MSR_LS_CFG		(11*32+19) /* "" MSR AMD64_LS_CFG */
>
>We already have that one:
>
>#define X86_FEATURE_LS_CFG_SSBD         ( 7*32+24)  /* "" AMD SSBD implementation via LS_CFG MSR */

Looking at bsp_init_amd() this feature bit will only be set on AMD
families 0x15-0x17. Andrew mentioned that the MSR LS_CFG is present on
AMD family >= 0x10 && family <= 0x18. That is why I added a new bit for
the MSR.