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

[Boris Ostrovsky]

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.

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.

-boris