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Re: [Xen-devel] [RFC PATCH 2/3] arch, arm32: add the XEN_DOMCTL_memory_mapping hypercall

On 03/07/2014 04:41 AM, Julien Grall wrote:
> Hello Arianna,
> On 07/03/14 08:56, Arianna Avanzini wrote:
>>>> Beware:  I found that map_mmio_regions was off by one page unless I changed
>>>> "gfn + nr_mfns - 1" to "gfn + nr_mfns".
>>>> This may have been fixed in more recent upstream code.
>>> That makes me think, map_mmio_regions is buggy if the range is not correctly
>>> aligned. For instance:
>>> start_gaddr = 0x1001 and end_gaddr = 0x2001, we only map 0x1000-0x2000 to 
>>> the
>>> domain.
>>> The problem is the same with p2m_populate_ram (even if I doubt that RAM 
>>> range is
>>> not page-aligned).
>>> I see 2 solutions to fix it:
>>>      - Change map_mmio_regions prototype to use frame is instead address.
>>>          - Aligned the input addresses.
>>> IHMO, the former seems to be better, at least it avoid developer to discover
>>> that some bits was mapped under his feet.
>> Sorry if I intrude here, thank you for pointing that out. As of now I have 
>> tried
>> to simply pass aligned addresses to map_mmio_regions() when it is invoked by 
>> the
>> memory_mapping hypercall.
> FYI, the end address should be PAGE-aligned minus 1. Otherwise you will map a
> spurious page to the guest.

Thank you for pointing that out.

>> Sorry for the additional question, do you think that it would be appropriate 
>> to
>> add to the series a patch implementing one of the above-described solutions 
>> (the
>> one believed to be better)?
> I'd like to have some input from Ian before. I think for now it's fine to stay
> with the current implementation.

OK. Thank you for making this clear.

> Regards,

 * Arianna Avanzini
 * avanzini.arianna@xxxxxxxxx
 * 73628@xxxxxxxxxxxxxxxxxxx

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