linux-kernel - Re: [PATCH v2 01/12] kexec: Allow architecture code to opt-out at runtime

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Date:   Tue, 2 Nov 2021 18:17:39 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Joerg Roedel <joro@...tes.org>, x86@...nel.org,
        kexec@...ts.infradead.org, Joerg Roedel <jroedel@...e.de>,
        stable@...r.kernel.org, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Martin Radev <martin.b.radev@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 01/12] kexec: Allow architecture code to opt-out at
 runtime

On Mon, Nov 01, 2021 at 04:11:42PM -0500, Eric W. Biederman wrote:
> I seem to remember the consensus when this was reviewed that it was
> unnecessary and there is already support for doing something like
> this at a more fine grained level so we don't need a new kexec hook.

Well, the executive summary is that you have a guest whose memory *and*
registers are encrypted so the hypervisor cannot have a poke inside and
reset the vCPU like it would normally do. So you need to do that dance
differently, i.e, the patchset.

If you try to kexec such a guest now, it'll init only the BSP, as Joerg
said. So I guess a single-threaded kdump.

And yes, one of the prominent use cases is kdumping from such a guest,
as distros love doing kdump for debugging.

I hope that explains it better.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette