linux-kernel - Re: [PATCH v2 00/12] x86/sev: KEXEC/KDUMP support for SEV-ES guests

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Message-ID: <YT941raolZvGTVR/@suse.de>
Date:   Mon, 13 Sep 2021 18:14:14 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Joerg Roedel <joro@...tes.org>, x86@...nel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.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 00/12] x86/sev: KEXEC/KDUMP support for SEV-ES guests

On Mon, Sep 13, 2021 at 09:02:38AM -0700, Dave Hansen wrote:
> On 9/13/21 8:55 AM, Joerg Roedel wrote:
> > This does not work under SEV-ES, because the hypervisor has no access
> > to the vCPU registers and can't make modifications to them. So an
> > SEV-ES guest needs to reset the vCPU itself and park it using the
> > AP-reset-hold protocol. Upon wakeup the guest needs to jump to
> > real-mode and to the reset-vector configured in the AP-Jump-Table.
> 
> How does this end up looking to an end user that tries to kexec() from a
> an SEV-ES kernel?  Does it just hang?

Yes, the kexec will just hang. This patch-set contains code to disable
the kexec syscalls in situations where it would not work for that
reason.

Actually with the changes to the decompressor in this patch-set the
kexec'ed kernel could boot, but would fail to bring up all the APs.

Regards,

	Joerg