linux-kernel - Re: [RFC PATCH 3/5] x86/kexec: Disable kexec/kdump on platforms with TDX partial write erratum

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Message-ID: <5e736c6d7794b8642d020350e302ead0d6ca13ae.camel@intel.com>
Date: Thu, 13 Mar 2025 17:18:26 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "tglx@...utronix.de" <tglx@...utronix.de>, "peterz@...radead.org"
	<peterz@...radead.org>, "mingo@...hat.com" <mingo@...hat.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "Huang, Kai" <kai.huang@...el.com>, "bp@...en8.de"
	<bp@...en8.de>, "kirill.shutemov@...ux.intel.com"
	<kirill.shutemov@...ux.intel.com>
CC: "ashish.kalra@....com" <ashish.kalra@....com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>, "sagis@...gle.com" <sagis@...gle.com>,
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Subject: Re: [RFC PATCH 3/5] x86/kexec: Disable kexec/kdump on platforms with
 TDX partial write erratum

On Thu, 2025-03-13 at 00:57 +0000, Huang, Kai wrote:
> > Continuing an internal discussion... A problem with the plan to more simply
> > start support for kexec by not supporting the errata platforms is that when
> > these platforms configure TDX they will lose kexec by default.
> > 
> > Probably a better default for a lot of kernels would be to have kexec work
> > by
> > default, and require opt-in to use TDX (and lose kexec). One idea was a
> > kernel
> > parameter be required to enable TDX on those platforms. But then we are
> > starting
> > to add complexity to avoid other complexity (the errata platform kexec
> > support).
> > 
> > Still, it may be a net win on complexity.
> 
> We can add a kernel parameter 'tdx_host={on|off}' and skip all TDX code (thus
> no
> erratum detection) when it is off.  I suppose it will be useful in general
> anyway even w/o the context of kexec.

What exactly are you thinking? Add a tdx_host parameter, but what is the default
behavior? When tdx_host=on with the errata, kexec must still be disabled, right?
Better to return an error, than proceed and crash.