Re: [PATCH v2 2/8] xen/x86: Improvements to build-time pagetable generation

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 24/02/16 11:24, Jan Beulich wrote:
>  >>> On 23.02.16 at 17:31, <andrew.cooper3@citrix.com> wrote:
>> * Additional comments, including size and runtime use.
>>  * Consistent use of idx, rather than a mix including pfn.
> I don't see anything wrong with this - when we have a PFN why
> should we not call it a PFN? As opposed to when we have a table
> index not representing the corresponding PFN.

In the case of l2_identmap, the logic is more clearly expressed in terms
of idx.  That leaves l1_identmap as the odd one out, where idx and pfn
are equally applicable.

>
>>  GLOBAL(l1_identmap)
>> -        pfn = 0
>> +        idx = 0
>>          .rept L1_PAGETABLE_ENTRIES
>>          /* VGA hole (0xa0000-0xc0000) should be mapped UC. */
>> -        .if pfn >= 0xa0 && pfn < 0xc0
>> -        .long (pfn << PAGE_SHIFT) | PAGE_HYPERVISOR_NOCACHE | MAP_SMALL_PAGES
>> +        .if idx >= 0xa0 && idx < 0xc0
>> +        .quad (idx << PAGE_SHIFT) | PAGE_HYPERVISOR_NOCACHE
>>          .else
>> -        .long (pfn << PAGE_SHIFT) | PAGE_HYPERVISOR | MAP_SMALL_PAGES
>> +        .quad (idx << PAGE_SHIFT) | PAGE_HYPERVISOR
> Please don't eliminate the MAP_SMALL_PAGES here, they serve an
> (at least documentation) purpose.

How?  Its in a l1 so are necessarily small pages, and the other l1's
don't use the constant.

~Andrew