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

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Tue, Mar 21, 2017 at 10:01:15AM +0000, Roger Pau Monne 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.
> 
> What issues do you see when using the HVM boot path for kexec?

FWIW, I'm wondering what would it take to unify the HVM/PVH paths inside of
Linux. The PVH entry point is still needed in case Linux is booted without any
firmware, but that should just setup the page-tables and jump into the native
entry point, where it should join with the HVM code path if possible.

Roger.

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