Re: [Qemu-devel] [PATCH memory v1 1/1] memory: remove may_overlap property

[Peter Crosthwaite <peter.crosthwaite@xilinx.com>]

On Mon, Aug 18, 2014 at 5:23 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 18 August 2014 01:14, Peter Crosthwaite <peter.crosthwaite@xilinx.com> wrote:
>> On Mon, Aug 18, 2014 at 8:23 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
>>> On 15 August 2014 08:17, Peter Crosthwaite <peter.crosthwaite@xilinx.com> wrote:
>>>> If we were to repair this, a simpler and more effective check would be
>>>> to only assert collisions between same-priority regions. The fact that
>>>> colliding memory regions may-overlap is then left as implicit by the
>>>> fact that they have different priorities.
>>>
>>> I'm not sure your suggestion here would work, because priorities
>>> are only significant relative to other regions within the same
>>> container, whereas collisions can occur between two regions
>>> which don't have the same parent container and whose priorities are
>>> therefore not comparable. (For instance, consider [ A [ B C ] ]
>>> where A and B end up overlapping.)
>
>> But that is not a problem that is solved by the old may_overlap flag
>> is it? The check deleted here is not hierarchy aware so we have never
>> been able to detect that case. I think we should take a "clean slate"
>> approach on the implementation of the collision detection. Big change
>> is needed to get the check in the right place in code, whether it's
>> same-priority based or using may_overlap.
>
> Oops, I mistakenly thought this check was happening at the
> flattened-ranges point, but it's done when a subregion is
> added to a container. Maybe you're right that we should be
> able to allow overlaps if the priorities are different and not
> otherwise, then. But I'd rather we actually did that rather than
> just removing the check completely.
>

Right can we call it follow up though and get a merge on this one so
we can start fresh? With your new hierarchy problem we are just
compounding the reasons to get rid of this code.

Regards,
Peter

> thanks
> -- PMM
>