Re: [Xen-devel] [PATCH xen-4.6] xen: Remove CONFIG_X86_SUPERVISOR_MODE_KERNEL as x86_32 builds are unsupported

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Mon, 5 Jan 2015 15:35:27 +0000
Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

> On 05/01/15 15:16, Ian Campbell wrote:
> > On Fri, 2015-01-02 at 19:12 +0000, Andrew Cooper wrote:
> >> supervisor_mode_kernel was an x86_32-only feature which permitted
> >> a PV dom0 to run in ring 0, but at the expense of not being able
> >> to start any domUs.
> >>
> >> As the x86_32 Xen build has been removed from tree, removing the
> >> remaining supervisor_mode_kernel code.
> >>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >> CC: Keir Fraser <keir@xxxxxxx>
> >> CC: Jan Beulich <JBeulich@xxxxxxxx>
> >> CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >> CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> >> CC: Tim Deegan <tim@xxxxxxx>
> >>
> >> ---
> >>
> >> One complication is that PVH has reused
> >> XENFEAT_supervisor_mode_kernel with a modified meaning, and the
> >> Linux PVH code actively uses the flag as to indicate running as a
> >> PVH guest.
> > What is the modification? Doesn't a PVH kernel just use it to
> > indicate that it should (or wants) run in ring0 instead of
> > ring1/ring3? That was the original intention IIRC.

That flag has confused me too, and it was added later to pvh. 
Since, PVH guest is able to run in ring 0 ir-respective of the flag,
imho, XENFEAT_supervisor_mode_kernel can be just removed. The important
ones are really:

XENFEAT_auto_translated_physmap
XENFEAT_hvm_callback_vector

thanks
Mukesh


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