linux-kernel - RE: [EXTERNAL] Re: [PATCH 1/2] x86/Kconfig: Allow CONFIG_X86

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Message-ID: <PUZP153MB07490EDED3B0194F5518B26EBE4EA@PUZP153MB0749.APCP153.PROD.OUTLOOK.COM>
Date:   Fri, 2 Jun 2023 12:22:08 +0000
From:   Saurabh Singh Sengar <ssengar@...rosoft.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Saurabh Sengar <ssengar@...ux.microsoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: RE: [EXTERNAL] Re: [PATCH 1/2] x86/Kconfig: Allow CONFIG_X86_MPPARSE
 disable for OF platforms



> -----Original Message-----
> From: Dave Hansen <dave.hansen@...el.com>
> Sent: Thursday, May 25, 2023 7:26 PM
> To: Saurabh Singh Sengar <ssengar@...rosoft.com>; Saurabh Sengar
> <ssengar@...ux.microsoft.com>; tglx@...utronix.de; mingo@...hat.com;
> bp@...en8.de; dave.hansen@...ux.intel.com; x86@...nel.org;
> hpa@...or.com; KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; wei.liu@...nel.org; Dexuan Cui
> <decui@...rosoft.com>; Michael Kelley (LINUX) <mikelley@...rosoft.com>;
> linux-kernel@...r.kernel.org; linux-hyperv@...r.kernel.org
> Subject: Re: [EXTERNAL] Re: [PATCH 1/2] x86/Kconfig: Allow
> CONFIG_X86_MPPARSE disable for OF platforms
> 
> On 5/25/23 00:06, Saurabh Singh Sengar wrote:
> > When CONFIG_X86_MPPARSE is enabled, the kernel will scan low memory,
> > looking for MP tables. In Hyper-V VBS setup, lower memory is assigned to
> VTL0.
> > This lower memory may contain the actual MPPARSE table for VTL0, which
> > can confuse the VTLx kernel and cause issues. (x > 0)
> 
> This still just seems wrong.
> 
> If an action crashes the kernel because of changes, we don't just compile it
> out and move on.  We add enumeration for the new feature that's causing it
> and turn off the action at runtime.
> 

Thanks, I greatly appreciate your suggestion and wanted to let you know that
I am actively working on upstreaming the new fix for the VTL driver to bypass
the need for the MP table scan.

Furthermore, I would like to learn about the rationale behind disallowing the
disablement of CONFIG_X86_MPPARSE when MP tables are not in use. Considering
that we compile out the features we don't support, wouldn't it be acceptable to
allow users to customize their configurations in this manner? Allowing the
disablement of CONFIG_X86_MPPARSE would provide greater flexibility and
efficiency for those who do not utilize MP tables.