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

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Message-ID: <114b9d1593f1168072c145a0041c3bfe62f67a37.camel@intel.com>
Date: Mon, 27 Oct 2025 21:28:12 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "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"
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	"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, 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.