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

Dave Hansen
2021-09-13T16:21:32Z

On 9/13/21 9:14 AM, Joerg Roedel wrote:
> 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.

Got it. The end-user-visible symptom just wasn't obvious. If you
revise these, it might be nice to add that so that folks who cherry-pick
stable patches or update to new stable kernels have an idea what this
might fix.