Re: [Xen-devel] [PATCH 3/4 RFC] x86/p2m: use large pages for MMIO mappings

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.09.15 at 18:37, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 15/09/15 08:34, Jan Beulich wrote:
>> @@ -2044,22 +2078,45 @@ int map_mmio_regions(struct domain *d,
>>  {
>>      int ret = 0;
>>      unsigned long i;
>> +    unsigned int iter, order;
>>  
>>      if ( !paging_mode_translate(d) )
>>          return 0;
>>  
>> -    for ( i = 0; !ret && i < nr; i++ )
>> +    for ( iter = i = 0; i < nr && iter < MAP_MMIO_MAX_ITER;
>> +          i += 1UL << order, ++iter )
>>      {
>> -        ret = set_mmio_p2m_entry(d, start_gfn + i, _mfn(mfn + i),
>> -                                 p2m_get_hostp2m(d)->default_access);
>> -        if ( ret )
>> +        for ( order = mmio_order(d, (start_gfn + i) | (mfn + i), nr - i); ;
>> +              order = ret - 1 )
> 
> It is hard to reason as to whether this loop will terminate.  All it
> would take is a bug in set_mmio_p2m_entry() which causes it to
> unilaterally return 1 and this loop would never terminate.
> 
> Is there any other condition which can be used as a safety check?

I'm adding ASSERT()s as a minimal measure.

Jan


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