Re: [Qemu-devel] [PATCH 17/30] memory: add address_space_translate

[Jan Kiszka]

On 2013-05-27 10:19, Paolo Bonzini wrote:
> Il 27/05/2013 09:23, Jan Kiszka ha scritto:
>> On 2013-05-27 09:20, Paolo Bonzini wrote:
>>> Il 26/05/2013 11:02, Jan Kiszka ha scritto:
>>>>>>
>>>>>> Nice patches.  Only one thing, how is .impl.unaligned different
>>>>>> from the existing .valid.unaligned?
>>>> See memory.h: valid controls is an unaligned access traps or gets
>>>> processed, impl manages if it is passed as-is to the device or
>>>> broken up and aligned first.
>>>
>>> I took the following patches:
>>>
>>>     exec: Allow unaligned address_space_rw
>>>     exec: Resolve subpages in one step except for IOTLB fills
>>>     exec: Implement subpage_read/write via address_space_rw
>>>
>>> to limit the conflicts and because I realized that TCG should never
>>> encounter an IOMMU.
>>
>> Err, why? Will we emulate IOMMUs for TCG differently?
> 
> Because IOMMUs should never be added to address_space_memory.
> 
> TCG should only encounter an IOMMU during device emulation (DMA), not
> because of reads/writes from the CPU.  So the IOTLBs should never point
> to an IOMMU region.

OK. That's true for the current QEMU architecture, but may no longer be
like this if we once emulate device controllers via TCG (in hybrid
system setups). Anyway, I guess it's fine to optimize this for now.

Jan

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