Re: [Xen-devel] About booting Xen with UEFI on FastModel

[Chen Baozi <baozich@xxxxxxxxx>]

On Dec 18, 2013, at 19:59, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

> On Tue, 2013-12-17 at 23:57 +0800, Chen Baozi wrote:
>> On Tue 17 Dec 2013 06:12:21 PM CST, Ian Campbell wrote:
>>> On Tue, 2013-12-17 at 12:52 +0800, Chen Baozi wrote:
>>>> 3. Use smaller (e.g. 4K) page size in start-of-day page table.
>>> 
>>> This should work.
>> 
>> Personally, I prefer the 4K page size solution. But I'm not sure whehter
>> it would be appropriate to add a new level page table at first. I'll 
>> send
>> an experimental patch of it later this week.
> 
> Thanks. This is certainly not 4.4 material though I think so no rush.
> 
> The only real reason to avoid 4K pages and stick with 2M pages is the
> complexity in the asm code (since we need to populate them etc). They
> will also require space in the .bss (up to perhaps 512 pages for a full
> 2M span).
> 
> Ian.

I wrote a experimental patch allowing Xen to be loaded at a 4KB aligned
address using the 4KB page size solution. It has been tested on FastModel
and works.

However, after I finished this patch, I think it would be better to make
bootloader to load Xen on a 2M aligned address. There are mainly two
reasons:

1. As mentioned, it doesn’t increase the .bss size and avoid complexity in 
the asm code.

2. This patch still cannot deal with the situation where [paddr, paddr+2M)
and [vaddr, vaddr+2M) are overlapped but not aligned with the same size
(e.g., paddr = 0x80000 & vaddr = 0x200000).

So I guess a 2MB aligned load address is required in boot protocol?

Cheers,

Baozi

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