[PATCH][Xenial] UBUNTU: [Config] CONFIG_ARM64_VA_BITS=48

[Dann Frazier]

On Tue, Feb 2, 2016 at 6:04 AM, Tim Gardner <tim.gardner at canonical.com> wrote:
> On 02/02/2016 05:30 AM, Tim Gardner wrote:
>> On 02/01/2016 03:31 PM, dann frazier wrote:
>>> On Fri, Jan 29, 2016 at 06:23:35PM -0700, dann frazier wrote:
>>>> On NUMA implementations of Cavium ThunderX, node1 memory addresses start with
>>>> bit 40 set to 1, and therefore requires >= 41 bits of VA.
>>>>
>>>> Since we are using 4K pages, this also means moving from 3 to 4 level page
>>>> tables. The alternative would be increasing our page size. Upstream supports
>>>> 16K and 64K pages; 16K pages are not universally supported by ARM64 SoCs.
>>>>
>>>> 64K pages are pretty universal, but has issues of it's own:
>>>>   https://bugs.launchpad.net/skipper/+bug/1522204
>>>
>>> Oops - that should be: http://bugs.launchpad.net/bugs/1520162
>>>
>>
>> That bug makes it sound like we might be opening a can of worms with 64K
>> pages. Any thoughts on how much carnage this might cause ? Maybe we
>> should wait until binutils has been adjusted so that 4K applications are
>> 64K aligned ?
>>
>> rtg
>>
>
> Never mind. Paolo explained to me what this patch actually does. Could
> you add an annotation in debian.master/config/annotations so that we
> remember why we've made this change ?

Right, sorry - I was just trying to explain the other options we
considered before
choosing the 4K/4 level page table route.

I'll follow up w/ a patch that clarifies the text and adds an annotation.

  -dann

> rtg
>
> --
> Tim Gardner tim.gardner at canonical.com