Re: [Xen-devel] [Minios-devel] [PATCH 1/2] mini-os: support keeping start_info structure conditionally

[Juergen Gross <jgross@xxxxxxxx>]

On 29/08/16 13:47, Andrew Cooper wrote:
> On 29/08/2016 12:17, Juergen Gross wrote:
>> On 29/08/16 13:09, Wei Liu wrote:
>>> On Mon, Aug 29, 2016 at 01:01:08PM +0200, Juergen Gross wrote:
>>>> grub stubdom needs the start_info structure. Keep a copy of it in
>>>> pv mini-os if configured via "CONFIG_KEEP_STARTINFO". This should
>>>> default to "n" in order to have it enabled only when really needed.
>>>>
>>> I'm not sure I understand the rationale for this.
>>>
>>> Shouldn't start_info always be kept when mini-os is PV? Under what
>>> condition should it not be kept?
>> The application on top of Mini-OS shouldn't depend on Mini-OS being
>> paravirtualized or not in the "normal" case. grub-stubdom is a
>> special case, as it needs to kexec to a loaded kernel which in turn
>> needs the start_info, of course.
>>
>> ioemu-stubdom OTOH should not need start_info as it could work on
>> a HVMlite Mini-OS, too.
>>
>> The idea of removing start_info in my HVMlite series was driven by
>> that thought: any application using start_info should break as it
>> clearly wouldn't be agnostic of the mode (pv or HVMlite) of Mini-OS.
>> pv-grub was an oversight here.
>>
>> I'm planning to modify ioemu-stubdom in the future to not use
>> start_info and then let it run in HVMlite mode, too.
> 
> There is an issue here between MiniOS itself, and "the stubdom application".

Correct.

> There should be no circumstance where the stubdom application needs
> access (pv-grub being a special case, but maybe the kexec details can be
> hidden as well).

Indeed. I'll have a look if this is possible. In case I find a clean
solution I'll send patches including one removing CONFIG_KEEP_STARTINFO
again.

> However, while there is still relevant information in start_info, the
> low level PV bits should still have access.  Moreover, it is necessary
> to always have access when doing suspend/resume.

The information from start_info is available inside Mini-OS. So this
should be no problem.

Juergen

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