Re: [Xen-devel] [v7][RFC][PATCH 08/13] xen/x86/p2m: set p2m_access_n for reserved device memory mapping

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2014/10/30 17:24, Jan Beulich wrote:
> > > > On 30.10.14 at 08:39, <tiejun.chen@xxxxxxxxx> wrote:
> > On 2014/10/29 17:20, Jan Beulich wrote:
> > > Getting closer. Just set a to p2m->default_access before the if(),
> > > and overwrite it when rc == 1 inside the if(). And properly handle
> > > the error case (just logging a message - which btw lacks a proper
> > > XENLOG_G_* prefix - doesn't seem enough to me).
> > Please check the follows:
> >
> > @@ -686,8 +686,22 @@ guest_physmap_add_entry(struct domain *d, unsigned long 
> > gfn,
> >        /* Now, actually do the two-way mapping */
> >        if ( mfn_valid(_mfn(mfn)) )
> >        {
> > -        rc = p2m_set_entry(p2m, gfn, _mfn(mfn), page_order, t,
> > -                           p2m->default_access);
> > +        rc = 0;
> > +        a =  p2m->default_access;
> > +        if ( !is_hardware_domain(d) )
> > +        {
> > +            rc = 
> > iommu_get_reserved_device_memory(p2m_check_reserved_device_memory,
> > +                                                  &gfn);
> > +            /* We need to set reserved device memory as p2m_access_n. */
> > +            if ( rc == 1 )
> > +                a = p2m_access_n;
> > +            else if ( rc < 0 )
> > +                printk(XENLOG_WARNING
> > +                       "Domain %d can't check reserved device memory.\n",
> > +                       d->domain_id);
> > +        }
> > +
> > +        rc = p2m_set_entry(p2m, gfn, _mfn(mfn), page_order, t, a);
> >            if ( rc )
> >                goto out; /* Failed to update p2m, bail without updating m2p. */
> The handling of "a" looks good now, but the error handling and
> logging is still as broken as it was before.
Do you mean I'm missing some necessary info? Like gfn and mfn, so domain 
id, gfn and mfn can show enough message.
Sorry I'm poor to understand what you expect.

> > > But then again this code may change altogether if you avoid
> > > populating the reserved regions in the first place.
> > Are you saying this scenario?
> >
> > #1 Here we first set these ranges as p2m_access_n
> > #2 We reset them as 1:1 RMRR mapping with p2m_access_rw somewhere
> > #3 Someone may try to populate these ranges again
> No. I pointed at the fact that if you avoid populating the holes,
> there's no need to force them to p2m_access_n. Any attempts
> to map other than the 1:1 thing there could then simply be
> rejected.
I think any population should be rejected totally, because 1:1 mapping 
means guest can access these RMRR ranges in case of no any device 
assignment with RMRR, right? Any access to these range corrupt the real 
device usage.
Thanks
Tiejun

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