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: <e1b3da33446178861ca34e61675f184b439101e2.camel@intel.com>
Date: Thu, 13 Mar 2025 00:57:48 +0000
From: "Huang, Kai" <kai.huang@...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>, "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
	"bp@...en8.de" <bp@...en8.de>, "kirill.shutemov@...ux.intel.com"
	<kirill.shutemov@...ux.intel.com>
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	<ashish.kalra@....com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [RFC PATCH 3/5] x86/kexec: Disable kexec/kdump on platforms with
 TDX partial write erratum

On Wed, 2025-03-12 at 23:27 +0000, Edgecombe, Rick P wrote:
> On Thu, 2025-03-13 at 00:34 +1300, Kai Huang wrote:
> > The impact to userspace is the users will get an error when loading the
> > kexec/kdump kernel image:
> > 
> >   kexec_load failed: Operation not supported
> > 
> > This might be confusing to the users, thus also print the reason in the
> > dmesg:
> > 
> >   [..] kexec: not allowed on platform with tdx_pw_mce bug.
> 
> 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.