Re: [Xen-devel] [PATCH v12 5/6] x86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 4/7/2017 5:40 PM, Jan Beulich wrote:
> > > > On 06.04.17 at 17:53, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/mm/p2m-ept.c
> > +++ b/xen/arch/x86/mm/p2m-ept.c
> > @@ -544,6 +544,12 @@ static int resolve_misconfig(struct p2m_domain *p2m, 
> > unsigned long gfn)
> >                       e.ipat = ipat;
> >                       if ( e.recalc && p2m_is_changeable(e.sa_p2mt) )
> >                       {
> > +                         if ( e.sa_p2mt == p2m_ioreq_server )
> > +                         {
> > +                             ASSERT(p2m->ioreq.entry_count > 0);
> > +                             p2m->ioreq.entry_count--;
> > +                         }
> > +
> >                            e.sa_p2mt = p2m_is_logdirty_range(p2m, gfn + i, gfn 
> > + i)
> >                                        ? p2m_ram_logdirty : p2m_ram_rw;
> I don't think this can be right: Why would it be valid to change the
> type from p2m_ioreq_server to p2m_ram_rw (or p2m_ram_logdirty)
> here, without taking into account further information? This code
> can run at any time, not just when you want to reset things. So at
> the very least there is a check missing whether a suitable ioreq
> server still exists (and only if it doesn't you want to do the type
> reset).
Also I do not think we need to check if a suitable ioreq server still 
exists. We have guaranteed
in our patch that no new ioreq server will be mapped as long as the p2m 
table is not clean. :)
Yu

[snip]

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