Re: [Qemu-devel] [PATCH v2 1/2] exec: add page_mask for flatview_do_translate

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/10/2017 14:46, Maxime Coquelin wrote:
>>>           addr = ((iotlb.translated_addr & ~iotlb.addr_mask)
>>>                   | (addr & iotlb.addr_mask));
>>> -        *plen = MIN(*plen, (addr | iotlb.addr_mask) - addr + 1);
>>> +        page_mask = iotlb.addr_mask;
>>
>> Should this be "page_mask &= iotlb.addr_mask"?
>>
>> If you have multiple IOMMUs on top of each other (yeah, I know...) I
>> think the smallest size should win.  This is also consistent with the
>> MIN in the line below.
> 
> I agree, but changin to "page_mask &= iotlb.addr_mask" will not be
> enough, we also have to change the init value. Else we will always end
> up with 0xfff.
> 
> Maybe we could do as plen was handled before, i.e. setting page_mask
> init value to (hwaddr)(-1), and after the loop set it to
> ~TARGET_PAGE_MASK if it hasn't been changed.
> 
> Does that sound reasonable?

True that, in fact it makes sense for the "IOTLB entry" to represent all
of memory if there's no IOMMU at all.

Thanks,

Paolo