Re: About booting Xen with UEFI on FastModel

[Chen Baozi <baozich@gmail.com>]

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:
>> On Dec 11, 2013, at 19:29, Ian Campbell <Ian.Campbell@citrix.com> wrote:
>>
>>> On Wed, 2013-12-11 at 19:06 +0800, Chen Baozi wrote:
>>>> On Dec 11, 2013, at 18:59, Ian Campbell <Ian.Campbell@citrix.com> wrote:
>>>>
>>>>> On Wed, 2013-12-11 at 13:06 +0800, Chen Baozi wrote:
>>>>>> Hi Ian,
>>>>>>
>>>>>> On Dec 9, 2013, at 23:35, Ian Campbell <Ian.Campbell@citrix.com> wrote:
>>>>>>
>>>>>>> On Mon, 2013-12-09 at 23:15 +0800, Chen Baozi wrote:
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> I noticed that upstream UEFI is now supported ARMv8 on FastModel.
>>>>>>>> I’ve tried it to boot Linux with it. And it works. But it seems
>>>>>>>> it still cannot load Xen hypervisor properly. I’m now looking for
>>>>>>>> the reasons. Is there any difference for a firmware to load Xen
>>>>>>>> and Linux kernel?
>>>>>>>
>>>>>>> I think you are the first one to try Xen on EFI.
>>>>>>>
>>>>>>> Are you using the EFI stub with Linux or are you launching via a
>>>>>>> bootloader e.g. Grub-EFI?
>>>>>>
>>>>>> After reading the source code, I think it is neither the EFI stub
>>>>>> or a bootloader. A Linux Loader EFI application has been developed
>>>>>> for ARM in EFI.
>>>>>
>>>>> Do you have a link? I'm curious.
>>>>
>>>> Instructions to EFI on AArch64:
>>>>
>>>> http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=ArmPlatformPkg/AArch64
>>>>
>>>> And I’m using the git clone of its svn repository:
>>>>
>>>> https://github.com/tianocore/edk2.git
>>>>
>>>> Under the tree, the Linux Loader locates at:
>>>>
>>>> ArmPkg/Application/LinuxLoader
>>>
>>> Ah that, yes I think that boots Linux using the zImage protocol.
>>>
>>>>>
>>>>>> It is able to boot Linux either by tagged list or
>>>>>> dtb method. However, it hardcoded the start address of 0x80000
>>>>>> when loading Linux kernel, which make it unworkable for Xen after
>>>>>> paging is enable.
>>>
>>> 0x80000 is a problem due to the alignment not being 2M I think?
>>>
>>> Really should look into fixing that. (would probably mean allowing Xen
>>> to span 2 consecutive 2MB blocks and some additional fiddling during
>>> bring up)
>>
>> Yes, it is. I hacked EFI to make it boot Xen with a 2M aligned address.
>> And it seems to be OK.
>>
>> But I’m afraid it is not simply allowing Xen to span 2 consecutive 2MB
>> blocks, for it cannot deal with the different offsets within the page
>> ( 0x80080000 % 2M != 0x80200000 % 2M).
>>
>> IMHO, there might be 3 ways to solve this problem:
>>
>> 1. If Xen bootstrap code detected it at an address not aligned with
>> 2MB, then it copies itself to (x19 + 4M)\2M.
>
> This runs the risk of overwriting one of the other boot modules or
> something we need later and would have to happen before we had parsed
> the DTB to find out where those things are.
>
> We could mandate that there is space between the end of Xen and other
> stuff, but then we could probably just fix the load address too.
>

Is there any consideration not to make the load address offset same with
Linux (0x80000)? Because of memory layout?

>> 2. Modify LinuxLoader of EFI to load zImage at 2M aligned address.
>
> It's not impossible that we will end up with a XenLoader EFI anyway.
>

Is a XenLoader EFI necessary in future? Or there would be finally a 
bootloader
such as grub on ARM64?

>> 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.

Cheers,

Baozi

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