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

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Message-ID: <CAGtprH-mb0Cw+OzBj-gSWenA9kSJyu-xgXhsTjjzyY6Qi4E=aw@mail.gmail.com>
Date: Tue, 30 Sep 2025 19:05:38 -0700
From: Vishal Annapurve <vannapurve@...gle.com>
To: Dave Hansen <dave.hansen@...el.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 Tue, Sep 30, 2025 at 2:32 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 9/29/25 18:38, Vishal Annapurve wrote:
> >> On those platforms, the old kernel must reset TDX private memory before
> >> jumping to the new kernel, otherwise the new kernel may see unexpected
> >> machine check.  Currently the kernel doesn't track which page is a TDX
> >> private page.  For simplicity just fail kexec/kdump for those platforms.
> > Google has a usecase that needs host kdump support on SPR/EMR
> > platforms. Disabling kdump disables the host's ability to dump very
> > critical information on host crashes altogether. Is Intel working on
> > enabling kdump support for platforms with the erratum?
>
> Nope.
>
> Any workarounds are going to be slow and probably imperfect. That's not

Do we really need to deploy workarounds that are complex and slow to
get kdump working for the majority of the scenarios? Is there any
analysis done for the risk with imperfect and simpler workarounds vs
benefits of kdump functionality?

> a great match for kdump. I'm perfectly happy waiting for fixed hardware
> from what I've seen.

IIUC SPR/EMR - two CPU generations out there are impacted by this
erratum and just disabling kdump functionality IMO is not the best
solution here.