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: <e7b259b0a986f3cf1578b000f9113933ef80a324.camel@intel.com>
Date: Thu, 13 Mar 2025 22:47:38 +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>
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	<pbonzini@...hat.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 Thu, 2025-03-13 at 22:32 +0000, Huang, Kai wrote:
> > > 
> > > 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.
> 
> The default behaviour is tdx_host=off in order to not disrupt kexec/kdump
> behaviour on the TDX platforms with erratum.  The distros will be able to ship
> kernels with both CONFIG_KEXEC_CORE and CONFIG_INTEL_TDX_HOST on, and no
> visible
> impact to the user who doesn't care about TDX.
> 
> If the user is interested in TDX, tdx_host=on must be set in the kernel
> command
> line, but in this case user is expected to know kexec/kdump can only work
> normally if the TDX platform doesn't have the erratum -- kexec/kdump are
> disabled if the platform has the erratum.

So this will switch all of TDX to be default off then, unless the kernel gets a
parameter set. In which case we could also just unlock the Kconfig with just one
small change. TDX and kexec would still mutually exclusive, but just at runtime.
We should try to flag Paolo and see what he thinks.

Or is the proposal to only be default tdx_host=off on the errata platforms? And
tdx_host=on otherwise?

It seems like this series is close though, and would probably be wanted sooner
than later.