Re: [Xen-devel] [RFC PATCH 1/8]: PVH: Basic and preparatory changes

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Wed, 12 Sep 2012 19:26:20 +0100
Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

> On Wed, 2012-09-12 at 19:02 +0100, Mukesh Rathor wrote:
> > On Wed, 12 Sep 2012 09:12:25 +0100
> > Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > 
> > > On Tue, 2012-09-11 at 22:57 +0100, Mukesh Rathor wrote:
> > > > On Mon, 10 Sep 2012 14:55:52 +0100
> > > > Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > > It would likely be sufficient to just ifdef the bit which tells
> > > the builder that this kernel image supports PVH, which I guess is
> > > one or more XENFEATs in arch/x86/xen/xen-head.S?
> > > 
> > Nop, I've not added any new bits. Just using existing bits:
> > 
> > XENFEAT_writable_page_tables
> > XENFEAT_auto_translated_physmap
> > XENFEAT_supervisor_mode_kernel
> 
> Currently we declare:
>         ELFNOTE(Xen, XEN_ELFNOTE_FEATURES,       .asciz
> "!writable_page_tables|pae_pgdir_above_4gb")
> 
> It might be a mistake for writable_page_tables to be there already but
> in any case when you add the other two you should gate them on this
> new option.
> 
> (nb: "!foo" means "foo is required" rather than "not foo". I chose a
> very confusing character for this!)
> 
> It may also be worth having a XENFEAT_pvh for us in communicating
> support for this feature from the kernel to the tools (like
> XENFEAT_dom0). That's the opposite of case we wanted to avoid
> (enabling behaviour in the kernel).

Well, the way I have it is, it's the PV binary. To boot in PVH mode, you
put pvh=1 in vm.cfg file. The tool stacks read it and tell xen via
new flag XEN_DOMCTL_CDF_hybrid_guest. Err, make that _pvh_guest.
xen sets the new is_pvh bit in struct domain. The PVH guest upon boot
does xen_setup_features() first thing. xen sends it:

> XENFEAT_writable_page_tables
> XENFEAT_auto_translated_physmap
> XENFEAT_supervisor_mode_kernel
 
that with callback vector makes it a PVH guest. 

thanks,
mukesh

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