Re: [Xen-devel] [RFC][PATCH 12/13] hvmloader/pci: skip reserved ranges

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.05.15 at 10:16, <tiejun.chen@xxxxxxxxx> wrote:
> On 2015/5/15 15:44, Jan Beulich wrote:
>>>>> On 15.05.15 at 09:34, <tiejun.chen@xxxxxxxxx> wrote:
>>> So I think we may need to adjust pci_mem_start like this,
>>>
>>> @@ -301,6 +301,19 @@ void pci_setup(void)
>>>                pci_mem_start <<= 1;
>>>        }
>>>
>>> +    /* Relocate PCI memory that overlaps reserved space, like RDM. */
>>> +    for ( j = 0; j < memory_map.nr_map ; j++ )
>>> +    {
>>> +        if ( memory_map.map[j].type != E820_RAM )
>>> +        {
>>> +            reserved_end = memory_map.map[j].addr + memory_map.map[j].size;
>>> +            if ( check_overlap(pci_mem_start, pci_mem_end,
>>> +                               memory_map.map[j].addr,
>>> +                               memory_map.map[j].size) )
>>> +                pci_mem_start -= memory_map.map[j].size >> PAGE_SHIFT;
>>> +        }
>>> +    }
>>> +
>>>        if ( mmio_total > (pci_mem_end - pci_mem_start) )
>>>        {
>>>            printf("Low MMIO hole not large enough for all devices,"
>>>
>>> Right?
>>
>> I think that gets you in the right direction, but isn't enough, as it
>> doesn't account for (unavoidable) gaps (BARs are always a power
>> of 2 in size and accordingly aligned).
> 
> Right.
> 
> But as you see, we always take this action, >> PAGE_SHIFT, so this means 
> its always a sort of power of 2.

No, certainly not.

> Additionally, lets go back here,
> 
>          if ( (base < resource->base) || (base > resource->max) )
>          {
>              printf("pci dev %02x:%x bar %02x size "PRIllx": no space for "
>                     "resource!\n", devfn>>3, devfn&7, bar_reg,
>                     PRIllx_arg(bar_sz));
>              continue;
>          }
> 
> I mean even without rdm, the original codes don't consider handling this 
> lack of space from a alignment in advance, right?

Correct. But your change increases the chances of this getting
used. Also I think you may want to carefully look at under what
conditions this path gets taken without and with your patches.

Jan


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