Re: [Xen-devel] [PATCH v2 2/5] iommu: introduce dom0-iommu option

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf
> Of Roger Pau Monné
> Sent: 03 August 2018 09:14
> To: Jan Beulich <JBeulich@xxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>; Stefano Stabellini
> <sstabellini@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; George Dunlap
> <George.Dunlap@xxxxxxxxxx>; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Tim
> (Xen.org) <tim@xxxxxxx>; Julien Grall <julien.grall@xxxxxxx>; Suravee
> Suthikulpanit <suravee.suthikulpanit@xxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>; Brian Woods <brian.woods@xxxxxxx>
> Subject: Re: [Xen-devel] [PATCH v2 2/5] iommu: introduce dom0-iommu
> option
> 
> On Thu, Aug 02, 2018 at 02:23:23AM -0600, Jan Beulich wrote:
> > >>> On 02.08.18 at 09:46, <kevin.tian@xxxxxxxxx> wrote:
> > >>  From: Roger Pau Monne [mailto:roger.pau@xxxxxxxxxx]
> > >> Sent: Wednesday, August 1, 2018 7:04 PM
> > >> --- a/docs/misc/xen-command-line.markdown
> > >> +++ b/docs/misc/xen-command-line.markdown
> > >> @@ -1150,12 +1150,18 @@ detection of systems known to misbehave
> > >> upon accesses to that port.
> > >>
> > >>  > `dom0-passthrough`
> > >>
> > >> +> **WARNING: This command line option is deprecated, and
> superseded
> > >> by
> > >> +> _dom0-iommu=none_ - using both options in combination is
> > >> undefined.**
> > >> +
> > >
> > > in patch description you said 'supersede'... is it better to say that
> > > new dom0_iommu is favored if both options are specified than
> > > saying 'undefined'?
> >
> > That would complicate handling (perhaps just slightly, but anyway),
> > since we'd have to maintain a second boolean. Without that the
> > order on the command line determines behavior. (And I see that in
> > the end you've figured that out.)
> >
> > >> @@ -1198,6 +1204,32 @@ detection of systems known to misbehave
> upon
> > >> accesses to that port.
> > >>
> > >>  >> Enable IOMMU debugging code (implies `verbose`).
> > >>
> > >> +### dom0-iommu
> > >> +> `= List of [ none | strict | relaxed ]`
> > >> +
> > >> +> Sub-options are of boolean kind and can be prefixed with `no-` to
> effect
> > >> the
> > >> +> inverse meaning.
> > >
> > > not important comment, but doesn't "no-none" sound weird? :-)
> >
> > Only positive (true) values should be permitted for I think all of
> > these. I didn't look at the patch yes, so perhaps that's already
> > the case.
> 
> For the current set of options introduced in this patch none, strict
> or relaxed it doesn't make much sense to allow the no- prefix.
> 
> For options added in later patches (inclusive and reserved) it makes
> sense to allow the no- prefix, so that a user can do
> 'dom0-iommu=no-inclusive' in order to change the default value.
> 

But what does that mean? 'no-inclusive' clearly means you don't get the 
inclusive map, but what do you get instead? Strict? None?

  Paul

> I will make it clear which options allow the no- prefix, and add the
> code to parse such prefix when it's needed.
> 
> Roger.
> 
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