Re: [Xen-devel] Xen PVH support in grub2

[Juergen Gross <jgross@xxxxxxxx>]

On 06/11/17 15:51, Boris Ostrovsky wrote:
> On 11/06/2017 02:16 AM, Juergen Gross wrote:
>> On 03/11/17 20:00, Boris Ostrovsky wrote:
>>> On 11/03/2017 02:40 PM, Juergen Gross wrote:
>>>> On 03/11/17 19:35, Boris Ostrovsky wrote:
>>>>> On 11/03/2017 02:23 PM, Juergen Gross wrote:
>>>>>> On 03/11/17 19:19, Boris Ostrovsky wrote:
>>>>>>> On 11/03/2017 02:05 PM, Juergen Gross wrote:
>>>>>>>> So again the question: how to tell whether we are PVH or HVM in
>>>>>>>> init_hypervisor_platform()? ACPi tables are scanned way later...
>>>>>>> Can we make grub/OVMF append a boot option?
>>>>>>>
>>>>>>> Or set setup_header.hardware_subarch to something? We already have
>>>>>>> X86_SUBARCH_XEN but it is only used by PV.  Or we might be able to use
>>>>>>> hardware_subarch_data (will need to get a buy-in from x86 maintainers, I
>>>>>>> think).
>>>>>> But wouldn't this break the idea to reuse the native boot paths in
>>>>>> grub/OVMF without further modifications?
>>>>> WDYM? We will have to have some sort of a plugin in either one to build
>>>>> the zeropage anyway. So we'd set hardware_subarch there, in addition to
>>>>> other things like setting memory and such.
>>>> But isn't the zeropage already being built? I admit that setting subarch
>>>> isn't a big deal, but using another entry with a passed-through pvh
>>>> start struct isn't either...
>>> I don't follow, sorry. My understanding is that zeropage will be built
>>> by PVH-enlightened grub so part of this process would be setting the
>>> subarch bit.
>> My reasoning was based on Roger's remark:
>>
>> "OTOH if Linux is capable of booting from the native entry point inside
>> of a PVH container, we would only have to port OVMF and grub in order
>> to work inside of a PVH container, leaving the rest of the logic
>> untouched."
> 
> Right, and in my mind porting OVMF/grub includes creating proper zeropage.

Aah, okay. I reasoned on the assumption to just enable OVMF/grub to run
in PVH environment without touching the parts setting up anything for
the new kernel.

> BTW, another option might be to "type_of_loader = (9 << 4) | 0", which
> is what init_pvh_bootparams() does. In fact, whatever is done in the
> firmware should probably match what that routine does.

So it wouldn't be possible any longer to tell whether the kernel has
been booted directly or via grub. I don't like this. The loader type
is accessible via sysfs after all.


Juergen


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