Re: [Xen-devel] [PATCH v9 4/5] x86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

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

On 3/24/2017 6:37 PM, Jan Beulich wrote:
> > > > On 24.03.17 at 10:05, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > On 3/23/2017 5:00 PM, Jan Beulich wrote:
> > > > > > On 23.03.17 at 04:23, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > > > On 3/22/2017 10:29 PM, Jan Beulich wrote:
> > > > > > > > On 21.03.17 at 03:52, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > > > > > --- a/xen/arch/x86/hvm/ioreq.c
> > > > > > +++ b/xen/arch/x86/hvm/ioreq.c
> > > > > > @@ -949,6 +949,14 @@ int hvm_map_mem_type_to_ioreq_server(struct domain *d,
> > ioservid_t id,
> > > > > >     
> > > > > >         spin_unlock_recursive(&d->arch.hvm_domain.ioreq_server.lock);
> > > > > >     
> > > > > > +    if ( rc == 0 && flags == 0 )
> > > > > > +    {
> > > > > > +        struct p2m_domain *p2m = p2m_get_hostp2m(d);
> > > > > > +
> > > > > > +        if ( read_atomic(&p2m->ioreq.entry_count) )
> > > > > > +            p2m_change_entry_type_global(d, p2m_ioreq_server, p2m_ram_rw);
> > > > > > +    }
> > > > > If you do this after dropping the lock, don't you risk a race with
> > > > > another server mapping the type to itself?
> > > > I believe it's OK. Remaining p2m_ioreq_server entries still needs to be
> > > > cleaned anyway.
> > > Are you refusing a new server mapping the type before being
> > > done with the cleanup?
> > No. I meant even a new server is mapped, we can still sweep the p2m
> > table later asynchronously.
> > But this reminds me other point - will a dm op be interrupted by another
> > one, or should it?
> Interrupted? Two of them may run in parallel on different CPUs,
> against the same target domain.
Right. That's possible.

> > Since we have patch 5/5 which sweep the p2m table right after the unmap
> > happens, maybe
> > we should refuse any mapping requirement if there's remaining
> > p2m_ioreq_server entries.
> That's what I've tried to hint at with my question.
Oh. I see. Thank you, Jan. :-)

Yu
> Jan
>
>
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