Re: [PATCH v3 5/7] xen: add new domctl get_changed_domain

[Jürgen Groß <jgross@xxxxxxxx>]

On 16.12.24 11:41, Jan Beulich wrote:
> On 13.12.2024 17:24, Juergen Gross wrote:
> > --- a/xen/common/domain.c
> > +++ b/xen/common/domain.c
> > @@ -193,6 +193,57 @@ static void domain_changed_state(const struct domain *d)
> >       spin_unlock(&dom_state_changed_lock);
> >   }
> >   
> > +static void set_domain_state_info(struct xen_domctl_get_domain_state *info,
> > +                                  const struct domain *d)
> > +{
> > +    info->state = XEN_DOMCTL_GETDOMSTATE_STATE_EXIST;
> > +    if ( d->is_shut_down )
> > +        info->state |= XEN_DOMCTL_GETDOMSTATE_STATE_SHUTDOWN;
> > +    if ( d->is_dying == DOMDYING_dying )
> > +        info->state |= XEN_DOMCTL_GETDOMSTATE_STATE_DYING;
> > +    if ( d->is_dying == DOMDYING_dead )
> > +        info->state |= XEN_DOMCTL_GETDOMSTATE_STATE_DEAD;
> > +    info->unique_id = d->unique_id;
> > +}
> > +
> > +int get_domain_state(struct xen_domctl_get_domain_state *info, struct domain 
> > *d,
> > +                     domid_t *domid)
> > +{
> > +    unsigned int dom;
> > +
> > +    if ( info->pad0 || info->pad1 )
> > +        return -EINVAL;
> > +
> > +    if ( d )
> > +    {
> > +        set_domain_state_info(info, d);
> > +
> > +        return 0;
> > +    }
> > +
> > +    while ( (dom = find_first_bit(dom_state_changed, DOMID_MASK + 1)) <
> > +            DOMID_FIRST_RESERVED )
> > +    {
> > +        if ( test_and_clear_bit(dom, dom_state_changed) )
> For these two accesses to dom_state_changed don't you need to hold the
> lock patch 4 introduces? Also didn't you say you'd constrain the new
> sub-op to the sole domain having VIRQ_DOM_EXEC bound (which, ftaod,
> isn't enough to eliminate the race)?
Oh, indeed. Sorry for having missed both aspects.

> > +        {
> > +            *domid = dom;
> > +
> > +            d = rcu_lock_domain_by_id(dom);
> > +
> > +            if ( d )
> > +            {
> > +                set_domain_state_info(info, d);
> > +
> > +                rcu_unlock_domain(d);
> > +            }
> Oh, on the implicit "else" is where the original memset() would come into
> play: You want to make sure at least ->state, but perhaps also ->unique_id
> are cleared (rather than demanding the caller to clear them ahead of making
> the call).
Right.


Juergen

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