Re: [Xen-devel] [PATCH v1 0/8]: PVH (PV guest with extensions)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-10-03 at 21:39 +0100, Konrad Rzeszutek Wilk wrote:
> > You Ok with XEN_ELFNOTE_GUEST_PVH, or should I call it
> > XEN_ELFNOTE_PV_EXTENSIONS. Please LMK.

My intention was that you add XENFEAT_supervisor_mode_kernel et al. to
the existing XEN_ELFNOTE_FEATURES note rather than adding a whole new
note. I some how missed that this is what you were doing above. e.g.
what I meant was:

in Kconfig:
config XEN_X86_PVH
        bool "Support for running as a PVH guest (EXPERIMENTAL)"
        depends X86_64 && <..etc..> && EXPERIMENTAL
        help
                        This option enables support for running as a PVH
                        guest (PV guest using hardware extensions) under
                        a suitably capable hypervisor.
                        
                        This option is EXPERIMETNAL because the
                        hypervisor interfaces which it uses are not yet
                        considered stable therefore backwards and
                        forwards compatibility is not yet guaranteed.
                        
                        If unsure, say N.

Adjust the depends to suit reality.

I thought we had that second paragraph for ARM too, but it seems like I
was wrong, we should probably add it.

then in xen-head.S (adjusted for features actually used by PVH):
#ifdef CONFIG_XEN_X86_PVH
#define FEATURES_PVH "XENFEAT_writable_descriptor_tables|" \
                     "XENFEAT_auto_translated_physmap|" \
                     "XENFEAT_supervisor_mode_kernel" \
                     "XENFEAT_hvm_callback_vector"
#else
#define FEATURES_PVH /* Not supported */
#endif
...
ELFNOTE(Xen, XEN_ELFNOTE_FEATURES,       .asciz 
"!writable_page_tables|pae_pgdir_above_4gb"FEATURES_PVH)
...

I don't think we need to define a XENFEAT_pvh (or whatever it might be
called) since don't need it in the code so there's no need to define/use
it here. If/when we need something like that we can add it, or
preferably some more specific thing for the use case which crops up.

> XEN_ELFNOTE_PVH_FEATURES ?
> 
> That way you can fill it with different 'features' flags
> if need to. Say 1<<1 is basic, etc.

I don't think we need a PVH specific ELF note which just replicates the
XENFEAT infrastructure at this stage, if we do come to that then it
would be better to give PVH its own leaf in the existing feature space
(e.g. starting at 1*32+0).

Ian.



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