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

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Date:   Wed, 9 Nov 2022 22:09:03 -0800
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Andrew Cooper <Andrew.Cooper3@...rix.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        "antonio.gomez.iglesias@...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 Thu, Nov 10, 2022 at 12:00:11AM +0000, Andrew Cooper wrote:
>On 09/11/2022 17:37, Pawan Gupta wrote:
>> If SSBD is the only reason to restore MSR_AMD64_LS_CFG then we should be
>> able to use X86_FEATURE_LS_CFG_SSBD for enumeration.
>
>Yeah, although it occurs to me that you probably don't want to
>save/restore the whole MSR.  It's full of other things which want to
>stay in their current configuration.

Upstream currently saves and restores the whole MSR_AMD64_LS_CFG at
suspend/resume.

Is it that the configuration saved at suspend(other than SSBD) will not
be relevant at resume for this MSR? Is there any harm if keep the
current behavior?