linux-kernel - Re: [PATCH 4/7] x86/kexec: Disable kexec/kdump on platforms with TDX partial write erratum

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Message-ID: <2cbf11a4-fe92-483c-8ab7-182284720700@intel.com>
Date: Wed, 1 Oct 2025 11:00:16 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Vishal Annapurve <vannapurve@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, bp@...en8.de, tglx@...utronix.de, peterz@...radead.org,
 mingo@...hat.com, hpa@...or.com, thomas.lendacky@....com, x86@...nel.org,
 kas@...nel.org, rick.p.edgecombe@...el.com, dwmw@...zon.co.uk,
 kai.huang@...el.com, seanjc@...gle.com, reinette.chatre@...el.com,
 isaku.yamahata@...el.com, dan.j.williams@...el.com, ashish.kalra@....com,
 nik.borisov@...e.com, chao.gao@...el.com, sagis@...gle.com,
 farrah.chen@...el.com, Binbin Wu <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH 4/7] x86/kexec: Disable kexec/kdump on platforms with TDX
 partial write erratum

On 10/1/25 10:17, Vishal Annapurve wrote:
> And also mentions:
> "Also note only the normal kexec needs to worry about this problem, but
> not the crash kexec: 1) The kdump kernel only uses the special memory
> reserved by the first kernel, and the reserved memory can never be used
> by TDX in the first kernel; 2) The /proc/vmcore, which reflects the
> first (crashed) kernel's memory, is only for read.  The read will never
> "poison" TDX memory thus cause unexpected machine check (only partial
> write does)."
> 
> What was the scenario that led to disabling kdump support altogether
> given the above description?

I think it was purely out of convenience so that the disabling could be
three lines of code.

I don't know off the top of my head if there's a simple enough way to
disable kexec but not kdump. When I applied the thing, I was probably
just considering kexec/kdump a monolithic thing and not thinking that
folks would want one but not the other.

Kai, did you have any other motivations?