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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

>> 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.

Jan


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