Re: [PATCH] xen/arm: mm: fix nr_second calculation in setup_frametable_mappings

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

On 12/05/16 12:30, Peng Fan wrote:
> Hi Julien,
>
> On Thu, May 12, 2016 at 11:48:30AM +0100, Julien Grall wrote:
>> Hi Peng,
>>
>> On 12/05/16 07:36, Peng Fan wrote:
>>> To ARM64, "frametable_size >> SECOND_SHIFT" means the number
>>> of second level entries, not the number of second level pages.
>>>
>>> "DIV_ROUND_UP(frametable_size >> SECOND_SHIFT, LPAE_ENTRIES)"
>>> is the correct way to calculate the second level pages needed
>>> for frametable mapping.
>>
>> Good catch!
>>
>>> Signed-off-by: Peng Fan <van.freenix@gmail.com>
>>> Cc: Stefano Stabellini <sstabellini@kernel.org>
>>> Cc: Julien Grall <julien.grall@arm.com>
>>> ---
>>>   xen/arch/arm/mm.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
>>> index 0a4f845..7c7f8e9 100644
>>> --- a/xen/arch/arm/mm.c
>>> +++ b/xen/arch/arm/mm.c
>>> @@ -767,7 +767,7 @@ void __init setup_frametable_mappings(paddr_t ps, paddr_t pe)
>>>       base_mfn = alloc_boot_pages(frametable_size >> PAGE_SHIFT, 32<<(20-12));
>>>
>>>   #ifdef CONFIG_ARM_64
>>> -    nr_second = frametable_size >> SECOND_SHIFT;
>>> +    nr_second = DIV_ROUND_UP(frametable_size >> SECOND_SHIFT, LPAE_ENTRIES);
>>
>>
>> I think the following would be clearer:
>>
>> ROUNDUP(frametable_size, FIRST_SIZE) >> FIRST_SHIFT;
>
> Agree.
>
>>
>> This would also benefit a comment to explain that second level of page table
>> are populating.
>
> Do you mean I need to add a comment for the upper code?

Yes.

>
> For the commit log, I would like to change to this:
> "
> To ARM64, "frametable_size >> SECOND_SHIFT" means the number

On ARM64,

s/means/computes/


> of second level entries, not the number of second level pages.
>
> "ROUNDUP(frametable_size, FIRST_SIZE) >> FIRST_SHIFT" which means

s/means/computes/

> the number of the first level entries(the number of second level pages),

missing space after "entries"

> is the correct one that should be used.
> "

Regards,

-- 
Julien Grall

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