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

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Message-ID: <3cc285fc5f376763b7a0b02700ac4520e95cf4d6.camel@intel.com>
Date: Tue, 28 Oct 2025 09:31:34 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Annapurve, Vishal" <vannapurve@...gle.com>
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Subject: Re: [PATCH 4/7] x86/kexec: Disable kexec/kdump on platforms with TDX
 partial write erratum

On Mon, 2025-10-27 at 17:07 -0700, Vishal Annapurve wrote:
> 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?

I was thinking something like this:

https://lore.kernel.org/lkml/20250416230259.97989-1-kai.huang@intel.com/