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Re: [Xen-devel] [PATCH 05/10] xen/arm: vgic-v3: Document the current restrictions


On 21/01/15 13:19, Julien Grall wrote:
>>>>> If you give a look to the redistributor iniatialization (see Xen and
>>>>> Linux GICv3 code). The code will go through all the redistributors and
>>>>> check GICR_TYPER to see if the processor is associated to this
>>>>> redistributor.
>>>>> I'm not sure how the redistributor should behave if it's accessed by
>>>>> another processor.
>>>> Please can you find a spec reference and include it in the clarified
>>>> version of this item.
>>> Rather than the distributor, there is multiple redistributor (one per
>>> processor).
>>> I think the section 5.4.1 in the GICv3 should answer to this question:
>>> "Each re-distributor must be allocated at one page for controlling the
>>> overall behavior of the re-distributor and for controlling physical
>>> LPIs. The base address of this page is referred to as RD_base. In
>>> addition, each re-distributor must be also allocated the following
>>> additional pages".
>> That doesn't say anything about one CPU touching another's
>> redistributor.
> Linux is at least using GICR_TYPER, to retrieve the right distributor.
> For the other the register I've no idea. I've asked ARM. Let see what
> they will answer.

For documentation purpose, the re-distributor should be accessible by
any processor. It has been confirmed by ARM and I've found the paragraph
in spec stating:

"GICR_* registers. Multiple pages of registers per re-distributor
accessible to all processors." Section 4.3.5 of the r24 document.

I have a working implementation of this behavior. I will add it in the
v2 of this series and drop this patch.


Julien Grall

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