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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.02.16 at 14:57, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 24/02/16 11:24, Jan Beulich wrote:
>>  >>> On 23.02.16 at 17:31, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>  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.

MAP_SMALL_PAGES documents (and enforces) that the mappings
shouldn't be re-combined into 2M ones, even if - after adjustments
to the other attributes - they could be.

Jan


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