Re: [PATCH v3] xen: fix reboot/shutdown with running HVM guests

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 05/06/14 17:02, Jan Beulich wrote:
>>>> On 05.06.14 at 17:46, <andrew.cooper3@citrix.com> wrote:
>> On 05/06/14 16:01, Roger Pau Monne wrote:
>>> If there's a guest using VMX/SVM when the hypervisor shuts down, it
>>> can lead to the following crash due to VMX/SVM functions being called
>>> after hvm_cpu_down has been called. In order to prevent that, check in
>>> {svm/vmx}_ctxt_switch_from that the cpu virtualization extensions are
>>> still enabled.
>> I feel that this is still trying to fix the problem from the wrong end. 
>> It is incorrect to be in a context switch at the point identified in the
>> stack trace.
>>
>> How about having the hvm_cpu_down functions look at current, and
>> optionally run sync_exec_state() ?
> I considered this too before suggesting the other alternative,
> but why would getting into the context switch path this way
> be any better than through map_domain_page()?
>
> Jan
>

It is a more controlled point on all shutdown/crash paths, but still not
perfect.

What we probably need on all shutdown paths is an early step of
"reschedule the idle vcpu back on all pcpus".  This won't fix the issue
for crash paths however.

~Andrew