Re: [Xen-devel] [PATCH=v3 1/8] xen: arm: map memory as inner shareable.

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 03/17/2014 03:11 PM, Ian Campbell wrote:
> On Mon, 2014-03-17 at 15:06 +0000, Julien Grall wrote:
>> Hi Ian,
>>
>> On 03/17/2014 02:53 PM, Ian Campbell wrote:
>>> The inner shareable domain contains all SMP processors, including different
>>> clusters (e.g. big.LITTLE). Therefore this is the correct thing to use for 
>>> Xen
>>> memory mappings. The outer shareable domain is for devices on busses which 
>>> are
>>> coherent and barrier-aware (e.g. AMBA4 AXI with ACE). While the system 
>>> domain
>>> is for things behind bridges which are not.
>>>
>>> One wrinkle is that Normal memory with attributes Inner Non-cacheable, Outer
>>> Non-cacheable (which we call BUFFERABLE) must be mapped Outer Shareable on 
>>> ARM
>>> v7. Therefore change the prototype of mfn_to_xen_entry to take the attribute
>>> index so we can DTRT. On ARMv8 the sharability is ignored and considered to
>>> always be Outer Shareable.
>>>
>>> Don't adjust the barriers, flushes etc, those remain as they were (which is
>>> more than is now required).  I'll change those in a later patch.
>>>
>>> Many thanks to Leif for explaining the difference between Inner- and
>>> Outer-Shareable in words of two or less syllables, I hope I've replicated 
>>> that
>>> explanation properly above!
>>
>> Is there any reason to not modify VTCR_EL2?
> 
> Could do as a future cleanup but I wanted to get Xen's own mappings
> sorted first.

AFAIU, you are also modifying P2M attributes. In any case:

Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>

-- 
Julien Grall

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