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

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Message-ID: <811dc6c51bb4dfdc19d434f535f8b75d43fde213.camel@intel.com>
Date: Mon, 27 Oct 2025 00:50:42 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "Annapurve, Vishal"
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Subject: Re: [PATCH 4/7] x86/kexec: Disable kexec/kdump on platforms with TDX
 partial write erratum

On Sun, 2025-10-26 at 16:33 -0700, Vishal Annapurve wrote:
> > 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.
> 
> Hi Kai,

Hi Vishal,

> 
> 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.