Re: [for-4.7 1/2] xen: XENMEM_add_physmap_batch: Mark 'foreign_id' as reserved for dev_mmio

[Julien Grall <julien.grall@arm.com>]

Hi Jan,

On 25/05/16 14:12, Jan Beulich wrote:
>>>> On 25.05.16 at 13:41, <julien.grall@arm.com> wrote:
>> --- a/xen/arch/arm/mm.c
>> +++ b/xen/arch/arm/mm.c
>> @@ -1143,6 +1143,10 @@ int xenmem_add_to_physmap_one(
>>           break;
>>       }
>>       case XENMAPSPACE_dev_mmio:
>> +        /* The field 'foreign_domid' is reserved for future use */
>> +        if ( foreign_domid )
>> +            return -ENOSYS;
>
> This should return -EINVAL or maybe -EOPNOTSUPP, but
> definitely not -ENOSYS.

I will use -EOPNOTSUPP.

>
>> --- a/xen/common/memory.c
>> +++ b/xen/common/memory.c
>> @@ -639,9 +639,11 @@ static int xenmem_add_to_physmap(struct domain *d,
>>   {
>>       unsigned int done = 0;
>>       long rc = 0;
>> +    /* The field 'foreign_id' should be 0 when mapping MMIO. */
>> +    domid_t inv = (xatp->space != XENMAPSPACE_dev_mmio) ? DOMID_INVALID : 0;
>
> This is a bad type for something that now isn't a domain ID anymore.
> Please use u16 or even better unsigned int. Eventually we should
> fix xenmem_add_to_physmap_one()'s respective parameter type
> accordingly.
>
> Also I think the condition would better be space == gmfn_foreign.

Ok.

>
>> @@ -658,7 +660,7 @@ static int xenmem_add_to_physmap(struct domain *d,
>>
>>       while ( xatp->size > done )
>>       {
>> -        rc = xenmem_add_to_physmap_one(d, xatp->space, DOMID_INVALID,
>> +        rc = xenmem_add_to_physmap_one(d, xatp->space, inv,
>>                                          xatp->idx, xatp->gpfn);
>
> This instance you could actually leave alone (as it's dealing with
> XENMAPSPACE_gmfn_range only).
>
>> --- a/xen/include/public/memory.h
>> +++ b/xen/include/public/memory.h
>> @@ -259,7 +259,7 @@ struct xen_add_to_physmap_batch {
>>
>>       /* Number of pages to go through */
>>       uint16_t size;
>> -    domid_t foreign_domid; /* IFF gmfn_foreign */
>> +    domid_t foreign_domid; /* IFF gmfn_foreign. Should be 0 for other spaces. */
>
> I wonder whether we shouldn't fix up the structure here right away,
> instead of deferring that to after 4.7. After all, as above, we don't
> really want a domain ID here generally anymore, so this should
> either become "u16 aux" (or some such) or a union (all of course only
> for new enough __XEN_INTERFACE_VERSION__).
>
> Plus I think we will want this to be IN/OUT, such that if the
> implementation, rather than failing, uses a replacement attribute,
> that could be communicated back. Of course that would matter
> only if we don't go the union route mentioned above.

I will give a look to use an union.

Regards,
-- 
Julien Grall

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