Re: [PATCH for-4.17?] x86/paging: return -EINVAL for paging domctls for dying domains

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, Nov 09, 2022 at 11:23:01AM +0100, Jan Beulich wrote:
> On 09.11.2022 11:11, Roger Pau Monné wrote:
> > On Wed, Nov 09, 2022 at 08:48:46AM +0100, Jan Beulich wrote:
> >> Finally I'm not convinced of the usefulness of this dying check in the
> >> first place: is_dying may become set immediately after the check was
> >> done.
> > 
> > While strictly true, this code is executed with the domain lock held,
> > so while is_dying might change, domain_kill() won't make progress
> > because of the barrier on the domain lock just after setting is_dying.
> 
> I guess I'm confused now: This code is called with the domctl lock
> held, which - as said before - is a questionable thing, for serializing
> things more than necessary as well as for holding this lock for
> excessive periods of time. IOW I consider it wrong to depend on that
> in paging_domctl() to synchronize against domain_kill(). Yet indeed that
> should eliminate races at present.

Right, both are domctls.  There are other places where is_dying get
set as part of failures in the domain create paths, but then the
paging domctl failing would be natural, as the domain is being
destroyed as part of a failed domain create.

Since I don't see replies to my other comments, do you agree on
returning an error then?

Thanks, Roger.