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

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Message-ID: <CAGtprH9uhdwppnQxNUBKmA4DwXn3qwTShBMoDALxox4qmvF6_g@mail.gmail.com>
Date: Mon, 27 Oct 2025 17:07:14 -0700
From: Vishal Annapurve <vannapurve@...gle.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "pbonzini@...hat.com" <pbonzini@...hat.com>, "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, 
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "ashish.kalra@....com" <ashish.kalra@....com>, 
	"Hansen, Dave" <dave.hansen@...el.com>, "thomas.lendacky@....com" <thomas.lendacky@....com>, 
	"kas@...nel.org" <kas@...nel.org>, "seanjc@...gle.com" <seanjc@...gle.com>, 
	"dwmw@...zon.co.uk" <dwmw@...zon.co.uk>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "mingo@...hat.com" <mingo@...hat.com>, 
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "nik.borisov@...e.com" <nik.borisov@...e.com>, 
	"Chatre, Reinette" <reinette.chatre@...el.com>, "hpa@...or.com" <hpa@...or.com>, 
	"peterz@...radead.org" <peterz@...radead.org>, "sagis@...gle.com" <sagis@...gle.com>, 
	"Chen, Farrah" <farrah.chen@...el.com>, "tglx@...utronix.de" <tglx@...utronix.de>, 
	"bp@...en8.de" <bp@...en8.de>, "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>, 
	"Gao, Chao" <chao.gao@...el.com>, "x86@...nel.org" <x86@...nel.org>, 
	"Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH 4/7] x86/kexec: Disable kexec/kdump on platforms with TDX
 partial write erratum

On Mon, Oct 27, 2025 at 2:28 PM Huang, Kai <kai.huang@...el.com> wrote:
>
> On Mon, 2025-10-27 at 16:23 +0000, Edgecombe, Rick P wrote:
> > On Mon, 2025-10-27 at 00:50 +0000, Huang, Kai wrote:
> > > >
> > > > IIUC, kernel doesn't donate any of it's available memory to TDX module
> > > > if TDX is not actually enabled (i.e. if "kvm.intel.tdx=y" kernel
> > > > command line parameter is missing).
> > >
> > > Right (for now KVM is the only in-kernel TDX user).
> > >
> > > >
> > > > Why is it unsafe to allow kexec/kdump if "kvm.intel.tdx=y" is not
> > > > supplied to the kernel?
> > >
> > > It can be relaxed.  Please see the above quoted text from the changelog:
> > >
> > >  > It's feasible to further relax this limitation, i.e., only fail kexec
> > >  > when TDX is actually enabled by the kernel.  But this is still a half
> > >  > measure compared to resetting TDX private memory so just do the simplest
> > >  > thing for now.
> >
> > I think KVM could be re-inserted with different module params? As in, the two
> > in-tree users could be two separate insertions of the KVM module. That seems
> > like something that could easily come up in the real world, if a user re-inserts
> > for the purpose of enabling TDX. I think the above quote was talking about
> > another way of checking if it's enabled.
>
> Yes exactly.  We need to look at module status for that.

So, the right thing to do is to declare the host platform as affected
by PW_MCE_BUG only if TDX module is initialized, does that sound
correct?