Re: [Xen-devel] [PATCH for-4.10 4/5] tools/dombuilder: Fix asymetry when setting up console and xenstore rings

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Oct 05, 2017 at 07:23:42PM +0100, Andrew Cooper wrote:
> libxl always uses xc_dom_gnttab_init(), which internally calls
> xc_dom_gnttab{_hvm,}_seed() to set up the grants point at the console and
> xenstore rings.  For HVM guests, libxl then asks Xen for the information set
> up previously, and calls xc_dom_gnttab_hvm_seed() a second time, which is
> wasteful.  ARM construction expects libxl to have set up
> dom->{console,xenstore}_evtchn earlier, so only actually functions because of
> this second call.
> 
> Rationalise everything and make it consistent for all guests.
> 
>  1) Users of the domain builder are expected to provide
>     dom->{console,xenstore}_{evtchn,domid} unconditionally.  This is checked
>     by setting invalid values in xc_dom_allocate(), and checking in
>     xc_dom_boot_image().
> 
>  2) For x86 HVM and ARM guests, the event channels are given to Xen at the
>     same time as the ring gfns.  ARM already did this, but x86 is updated to
>     match.  x86 PV already provides this information in the start_info page.
> 
>  3) Libxl is updated to drop all relevent functionality from
>     hvm_build_set_params(), and behave consistently with PV guests when it
>     comes to the handling of dom->{console,xenstore}_{evtchn,domid,gfn}.
> 
> This removes several redundant hypercalls (including a foreign mapping) from
> the x86 HVM and ARM construction paths.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

With Roger's comments addressed:

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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