Re: [PATCH v1] xen/arm: Do not allocate pte entries for MAP_SMALL_PAGES

[Julien Grall <julien.grall@linaro.org>]

Hi Ian,

On 03/03/2015 10:27, Ian Campbell wrote:
> On Tue, 2015-03-03 at 13:28 +0530, Vijay Kilari wrote:
>> On Tue, Feb 24, 2015 at 6:29 PM, Julien Grall <julien.grall@linaro.org> wrote:
>>> On 24/02/15 10:26, Ian Campbell wrote:
>>>> On Tue, 2015-02-24 at 09:38 +0000, Julien Grall wrote:
>>>>> Hi Ian,
>>>>>
>>>>> On 24/02/2015 09:31, Ian Campbell wrote:
>>>>>> On Wed, 2015-02-18 at 13:03 +0000, Julien Grall wrote:
>>>>>>>> +                {
>>>>>>>> +                    pte = mfn_to_xen_entry(mfn, (ai & 0xffff));
>>>>>>>
>>>>>>> Please introduce a new macro for the mask.
>>>>>>
>>>>>> Better would be a pte_foo accessor, similar (if not identical) to x86's
>>>>>> pte_get_flags. So pte_get_flags(ai) or so.
>>>>>
>>>>> I'm not able to find a such function in x86. Did you intend to mean
>>>>> pte_flags_to_cacheattr?
>>>>
>>>> It's actually get_pte_flags.
>>>>
>>>>> In another side, using PTE_PRESENT would require to introduce a
>>>>> PAGE_AVAIL0 (or smth similar).
>>>>
>>>> Why?
>>>
>>> If we have only a bit PTE_PRESENT, how do you define MAP_SMALL_PAGES?
>>
>> MAP_SMALL_PAGES is already defined as WRITE_ALLOC which occupies lower 3 bits
>> what is need for PAGE_AVAIL0?
>>
>> Below definitions should suffice?
>
> I think so. You don't need the ()s around DEV_* and WRITE_ALLOC etc in
> the PAGE_* definitions.

I'm not sure to follow here. Do you think MAP_SMALL_PAGES should be 
defined as WRITE_ALLOC?


> A comment on the format of the bit packing done here would also be
> useful e.g. "16: present\n2:0: pte attributes field" in a little block
> comment above this stuff, below the DEV_* stuff.
>
> PAGE_PRESENT might be more in keepign that PTE_PRESENT, since this isn't
> a PTE bit pattern.

Sounds good to me.

Regards,

-- 
Julien Grall