linux-kernel - Re: [PATCH] x86/hyperv: add noop functions to x86

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Message-ID: <442441b3-803e-0c1f-ff1b-5a49ecc2e423@intel.com>
Date:   Fri, 2 Jun 2023 08:33:13 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Saurabh Sengar <ssengar@...ux.microsoft.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org,
        mikelley@...rosoft.com, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, hpa@...or.com
Subject: Re: [PATCH] x86/hyperv: add noop functions to x86_init mpparse
 functions

On 6/2/23 05:41, Saurabh Sengar wrote:
> In !ACPI system, there is no way to disable CONFIG_X86_MPPARSE.
> When CONFIG_X86_MPPARSE is enabled for VTL2, the kernel will
> scan low memory looking for MP tables. Don't allow this, because
> low memory is controlled by VTL0 and may contain actual valid
> tables for VTL0, which can confuse the VTL2 kernel.

Do you folks have a writeup of this VTL* setup anywhere?  I'm struggling
to grasp why VTL0 and VTL2 share the same address space and why they
would get confused by each other's data structures.

$ grep -r VTL[02] Documentation/
$

Either way, this is way better than the #ifdefs.  But the changelog is
kinda just gibberish to me.