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

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Date:   Fri, 2 Jun 2023 09:21:47 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Wei Liu <wei.liu@...nel.org>
Cc:     Saurabh Sengar <ssengar@...ux.microsoft.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, 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 09:17, Wei Liu wrote:
> On Fri, Jun 02, 2023 at 08:33:13AM -0700, Dave Hansen wrote:
>> 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.
> Dave, here is some public information about Virtual Trust Level.
> 
> https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/vsm#virtual-trust-level-vtl

Yeah, I can google too. ;)

Seriously, though.  I don't need an architecture document.  This is like
me asking how NMIs work in Linux and someone pointing me to the SDM
describing the hardware architecture.

I need to know about the Linux implementation of these VTL's, not the
overall VTL architecture.