Re: [Qemu-devel] [RFC PATCH qemu 3/4] memory: Share flat views and dispatch trees between address spaces

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/09/2017 07:55, Alexey Kardashevskiy wrote:
> On 12/09/17 01:30, Paolo Bonzini wrote:
>> On 11/09/2017 14:08, Alexey Kardashevskiy wrote:
>>>> Ok, this makes sense.  Maybe it should be a flatview rather than an
>>>> AddressSpaceDispatch (a FlatView is essentially a list of
>>>> MemoryRegionSections; attaching the ASD to the FlatView is more or less
>>>> an implementation detail).
>>> The helpers I converted from AddressSpace to AddressSpaceDispatch do use
>>> dispatch structure only and do not use FlatView so it seemed logical.
>>
>> Understood, but from a design POV FlatView makes more sense.
>>
>>> btw this address_space in MemoryRegionSection - it does not seem to make
>>> much sense in the PhysPageMap::sections array, it only makes sense when
>>> MemoryRegionSection uses as a temporary object when calling listeners. Will
>>> it make sense if we enforce MemoryRegionSection::address_space to be NULL
>>> in the array and not NULL when used temporary?
>>
>> memory_region_section_get_iotlb needs to access the AddressSpaceDispatch
>> for sections stored in the PhysPageMap array, because
>> memory_region_section_get_iotlb uses the ASD to compute the section index.
> 
> Ohhh, not extremely trivial, out of curiosity - is that iotlb encoding
> described anywhere?

No, I don't think so.

> Anyway, this can be simplified (or rather made more straightforward?) -
> tlb_set_page_with_attrs() can calculate the section index and pass it to
> memory_region_section_get_iotlb(). Still does not make much sense? It just
> looks quite useless to keep that address_space pointer alive just for one
> case which can easily avoid using this pointer.

Hmm I suppose address_space_translate_for_iotlb knows the ASD and could
also return the index, basically combining it and
memory_region_section_get_iotlb() into one function.

Paolo