Re: [Xen-devel] [PATCH v7 4/5] ix86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

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

On 3/11/2017 12:03 AM, Jan Beulich wrote:
> > > > On 08.03.17 at 16:33, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/mm/p2m.c
> > +++ b/xen/arch/x86/mm/p2m.c
> > @@ -954,6 +954,26 @@ int p2m_change_type_one(struct domain *d, unsigned long 
> > gfn,
> >                            p2m->default_access)
> >            : -EBUSY;
> >   
> > +    if ( !rc )
> > +    {
> > +        switch ( nt )
> > +        {
> > +        case p2m_ram_rw:
> > +            if ( ot == p2m_ioreq_server )
> > +            {
> > +                p2m->ioreq.entry_count--;
> > +                ASSERT(p2m->ioreq.entry_count >= 0);
> > +            }
> > +            break;
> > +        case p2m_ioreq_server:
> > +            if ( ot == p2m_ram_rw )
> > +                p2m->ioreq.entry_count++;
> I don't think the conditional is needed here. If anything it should be
> an ASSERT() imo, as other transitions to p2m_ioreq_server should
> not be allowed.
Thanks, Jan. I'll use ASSERT.

> But there's a wider understanding issue I'm having here: What is
> an "entry" here? Commonly I would assume this to refer to an
> individual (4k) page, but it looks like you really mean table entry,
> i.e. possibly representing a 2M or 1G page.
Well, it should be an entry pointing to a 4K page(only).
For p2m_ioreq_server, we shall not meet huge page. Because they are 
changed from p2m_ram_rw pages
in set_mem_type() -> p2m_change_type_one(), which calls p2m_set_entry() 
with PAGE_ORDER_4K specified.

Thanks
Yu
> Jan

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