Linux Virtualization - Sep 2021 - [PATCH v2 00/12] x86/sev: KEXEC/KDUMP support for SEV-ES guests

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?

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