Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <13922610-b9bc-ab4b-8482-9aae238396c7@intel.com>
Date:   Thu, 25 May 2023 06:56:10 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.11.0
Subject: Re: [EXTERNAL] Re: [PATCH 1/2] x86/Kconfig: Allow CONFIG_X86_MPPARSE
 disable for OF platforms
Content-Language: en-US
To:     Saurabh Singh Sengar <ssengar@microsoft.com>,
        Saurabh Sengar <ssengar@linux.microsoft.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
References: <1683816877-10747-1-git-send-email-ssengar@linux.microsoft.com>
 <9b88ddaf-c5c5-0244-5be7-12400ee54e11@intel.com>
 <PUZP153MB074959D2F85EAD559ED7B544BE41A@PUZP153MB0749.APCP153.PROD.OUTLOOK.COM>
 <33d7800b-7870-6755-b057-f734fa7accd6@intel.com>
 <PUZP153MB074988C9F8F891533871173BBE46A@PUZP153MB0749.APCP153.PROD.OUTLOOK.COM>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <PUZP153MB074988C9F8F891533871173BBE46A@PUZP153MB0749.APCP153.PROD.OUTLOOK.COM>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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.