Re: [PATCH] memory: Do not allow subregion out of the parent region range

[Richard Henderson]

On 12/17/19 1:58 AM, Christophe de Dinechin wrote:
> 
> 
>> On 17 Dec 2019, at 11:51, Paolo Bonzini <address@hidden> wrote:
>>
>> On 16/12/19 18:46, Philippe Mathieu-Daudé wrote:
>>>>>
>>>>
>>>> I think in some cases this could be intentional, for example if you have
>>>> different models with different BAR sizes and you organize this with the
>>>> same tree of MemoryRegion and different sizes for the parent.
>>>
>>> But if a child is outside of the parent range, it can't be reached,
>>> right? I'm confused, maybe AddressSpace can do that, but MemoryRegion
>>> shouldn't?
>>
>> Yes, the idea is that you could have for one version of the device
>>
>>   parent 0x000-0x7ff
>>     stuff 0x000-0x3ff
>>     morestuff 0x400-0x7ff
>>
>> and for another
>>
>>   parent 0x000-0x3ff
>>     stuff 0x000-0x3ff
>>     morestuff 0x400-0x7ff
>>
>> where parent is the BAR, and you can share the code to generate the tree
>> underneath parent.
> 
> I can see why you would have code reuse reasons to do that,
> but frankly it looks buggy and confusing. In the rare cases
> where this is indented, maybe add a flag making it explicit?

The guest OS is programming the BAR, producing a configuration that, while it
doesn't make sense, is also legal per PCI.  QEMU cannot abort for this
configuration.


r~