Re: XEN3_DOM0 rationalization

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

On Mar 7, 21:50, Manuel Bouyer wrote:
} On Sun, Mar 07, 2021 at 11:25:52AM -0800, John Nemeth wrote:
} > On Mar 7, 13:47, Greg Troxel wrote:
} > } 
} > } Right now I think people need to read the HOWTO to figure out how to set
} > } up Xen on NetBSD.  It's getting even more complicated with PVHVM and PVH
} > 
} >      Pretty much all complex software has some kind of learning
} > curve.  I really don't view this as a negative.  Would you expect
} > to be able to setup Asterisk, Samba, any other virtual environment,
} > etc.  without doing some reading?
} > 
} >      PVHVM and PVH are in their infancy and can be ignored by most
} > people for now.  I certainly wouldn't include them in the HOWTO at
} > this point,  Also, last I knew we hadn't done much at all with PVH.
} > The difference is PVHVM is domU running in HVM mode, but with access
} > to PV devices (much more efficient since device emulation isn't
} > needed).  Whereas PVH is for dom0 so that it runs in an HVM like
} > mode.
} 
} No, PVH is for domU: like PHVVM but without qemu in the dom0.
} This is mature on the Xen side, but not yet in a release on the NetBSD
} side.

     Hrmm, okay.  Pretty much every reference I've seen to PVH was
also a reference to dom0.  I see that the difference has to do with
interrupts and timers, and how the VM is booted.  With PVHVM, BIOS
style booting is used, which requires QEMU; whereas, with PVH, PV
style booting is used.

} dom0 can be run in PVH mode too, but this is still considered experimental
} on the Xen side (and only runs on a much more restried set of hardware than
} domU PVH). The support on the NetBSD side is not complete yet (dom0 can boot
} but the xentools don't work yet).

     On another note, it looks like Xen on ARM only supports one
mode that is very much like PVH (but not exactly).  This means that
it would be nice to get our PVH support completed so that we can
start looking at supporting Xen on ARM.

}-- End of excerpt from Manuel Bouyer