Re: [PATCH 2/2] xen: arm: Set all bits in mfn_to_xen_entry()

[Julien Grall <julien.grall@citrix.com>]

On 17/08/2015 11:58, Chris (Christopher) Brand wrote:
> Hi Julien,
>
> Thanks for the review.
>
>>> +            .pxn = 0,
>>
>> I would add a comment to explain that this bit is reserved for PL2 stage
>> 1 page table.
>
> Will do.
>
>>> +            .avail = 0,
>>
>> I don't think this one is necessary. avail is not used by the hardware neither
>> Xen.
>
> "grep -rF pt.avail xen" gives 7 matches in xen/arch/arm/mm.c, so it is used by
> Xen (I'll fully admit that I didn't dig in to the "how and why" of its use).

Hmmm right. Sorry I haven't check the Xen code for that.

It's used for domheap mapping to know how many times it has been referenced.

>
>> what about *t fields (pxnt, xnt, apt,...)?
>
> I figured that as we're setting table to 0, these are ignored, and any code setting
> table to 1 should then set them. I can obviously easily set them here (I guess all
> to zero would make sense) if you think it's worthwhile ...

It was just an open question. :) I'm not sure what we should do with them.

Regards,

-- 
Julien Grall