Re: [Xen-devel] [RFC] xen/pvh: detect PVH after kexec

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.03.17 at 11:21, <roger.pau@xxxxxxxxxx> wrote:
> On Tue, Mar 21, 2017 at 04:07:51AM -0600, Jan Beulich wrote:
>> >>> On 21.03.17 at 11:01, <roger.pau@xxxxxxxxxx> wrote:
>> > On Tue, Mar 21, 2017 at 10:21:52AM +0100, Vitaly Kuznetsov wrote:
>> >> Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> writes:
>> >> 
>> >> > On 03/20/2017 02:20 PM, Vitaly Kuznetsov wrote:
>> >> >> PVH guests after kexec boot like normal HVM guests and we're not 
>> >> >> entering
>> >> >> xen_prepare_pvh()
>> >> >
>> >> > Is it not? Aren't we going via xen_hvm_shutdown() and then
>> >> > SHUTDOWN_soft_reset which would restart at the same entry point as
>> >> > regular boot?
>> >> 
>> >> No, we're not doing regular boot: from outside of the guest we don't
>> >> really know where the new kernel is placed (as guest does it on its
>> >> own). We do soft reset to clean things up and then guest jumps to the
>> >> new kernel starting point by itself.
>> >> 
>> >> We could (in theory, didn't try) make it jump to the PVH starting point
>> >> but we'll have to at least prepare the right boot params for
>> >> init_pvh_bootparams and this looks like additional
>> >> complication. PVHVM-style startup suits us well but we still need to be
>> >> PVH-aware.
>> > 
>> > We are going to have the same issue when booting PVH with OVMF, Linux will 
> be
>> > started at the native UEFI entry point, and we will need some way to detect
>> > that we are running in PVH mode.
>> 
>> I'm confused: PVH boots without any firmware, doesn't it? Hence
>> it shouldn't matter if there's no (legacy) BIOS or no OVMF ...
> 
> Right now yes, we have no firmware available to PVH at all, but Anthony is
> already working on porting OVMF to PVH [0].

But that leaves open the "why" aspect: What use is OVMF to a
PVH guest?

Jan


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