linux-kernel - Re: [PATCH] x86/virt/tdx: Make TDX and kexec mutually exclusive at runtime

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Message-ID: <7bd03311-0c4c-41e6-b6dc-803b6455f170@intel.com>
Date: Thu, 17 Apr 2025 10:50:06 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Kai Huang <kai.huang@...el.com>, bp@...en8.de, tglx@...utronix.de,
 peterz@...radead.org, mingo@...hat.com
Cc: kirill.shutemov@...ux.intel.com, hpa@...or.com, x86@...nel.org,
 linux-kernel@...r.kernel.org, pbonzini@...hat.com, seanjc@...gle.com,
 rick.p.edgecombe@...el.com, reinette.chatre@...el.com,
 isaku.yamahata@...el.com, dan.j.williams@...el.com, thomas.lendacky@....com,
 ashish.kalra@....com, nik.borisov@...e.com, sagis@...gle.com
Subject: Re: [PATCH] x86/virt/tdx: Make TDX and kexec mutually exclusive at
 runtime

On 4/16/25 16:02, Kai Huang wrote:
> Full support for kexec on a TDX host would require complex work.
> The cache flushing required would need to happen while stopping
> remote CPUs, which would require changes to a fragile area of the
> kernel.

Doesn't kexec already stop remote CPUs? Doesn't this boil down to a
WBINVD? How is that complex?

> It would also require resetting TDX private pages, which is non-
> trivial since the core kernel does not track them.

Why? The next kernel will just use KeyID-0 which will blast the old
pages away with no side effects... right?

> Lastly, it would have to rely on a yet-to-be documented behavior
> around the TME key (KeyID 0).

I'll happily wait for the documentation if you insist on it (I don't).