Re: [Xen-devel] [PATCH-for-4.12] docs: Fix dm_restrict documentation

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Fri, Jan 25, 2019 at 04:10:55PM +0000, Wei Liu wrote:
> On Fri, Jan 25, 2019 at 02:47:20PM +0000, George Dunlap wrote:
> > On 1/25/19 11:33 AM, Wei Liu wrote:
> > > On Thu, Jan 24, 2019 at 05:48:27PM +0000, George Dunlap wrote:
> > >> Remove "chatty" and redundant information from the xl man page;
> > >> restrict it to functional descriptions only, and point instead to
> > >> qemu-depriv.pandoc and SUPPORT.md as locations for "canonical"
> > >> information.
> > >>
> > >> Add a man page entry for device_model_user.
> > >>
> > >> Update qemu-deprivilege.pandoc:
> > >>
> > >> Changes in missing feature list:
> > >> - Migration is functional
> > >> - But qdisk backends are not
> > >>
> > >> Add a missing restriction list.
> > >>
> > >> The following statements from the man page are dropped:
> > >> - Mentioning PV; PV guests never have a device model.
> > >> - Drop the confusing statement about stdvga and cirrus vga options.
> > >> - Re-used domain IDs are now handled.
> > >> - Device models should no longer be able to create world-readable
> > >>   files on dom0's filesystem.
> > >>
> > >> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> > >> ---
> > >> RFC: I don't know what the 'vga' limitation thing was about -- I tried
> > >> both 'default' and 'stgvga' with dm_restrict and they worked fine.
> > > 
> > > I think until we figure out the situation of vga, the statement should
> > > stay.
> > 
> > How would we do that?
> 
> Per my understanding:
> 
>   Setting vga option to anything else other than "none" may not work
> 
> ?

Is their an issue with the vga setting and dm_restrict=1 ? I never add
any problem. Accessing the guest graphic output via VNC while running
with dm_restrict works fine. (but I only ever use the default.)

Maybe it's time to blame! And do some archeology ...

Base on commit 7d278e2115d084a5f78a512ae01ce946c10cff7d
"xl: Document VGA problems arising from lack of physmap dmop"
the issue is just that using xc_domain_add_to_physmap doesn't work.

But that issue has been addressed with a new DMOPS, and QEMU have
support for it since:
commit 2cbf8903530b936964dd3af7e2e5bf85c3955d5c
"xen: Use newly added dmops for mapping VGA memory"
which is QEMU 3.0.

qemu-xen-4.12.0 is at least QEMU 3.0. So it should be just a matter of
documenting that we need QEMU 3.0.
But based on qemu-deprivilege.pandoc, QEMU 3.0 is required for
dm_restrict to works, so all is fine. The original mention of problem
with vga!=none isn't true anymore.

Version requirement is documented in the man page, which redirect to
qemu-deprivilege.pandoc which specify QEMU 3.0+. So all is fine.

Cheers,

-- 
Anthony PERARD

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