Re: [Xen-devel] [PATCH 2/4] iommu: generalize iommu_inclusive_mapping

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Roger Pau Monne
> Sent: 31 July 2018 10:35
> To: Jan Beulich <JBeulich@xxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap
> <George.Dunlap@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Paul
> Durrant <Paul.Durrant@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Kevin
> Tian <kevin.tian@xxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>
> Subject: Re: [Xen-devel] [PATCH 2/4] iommu: generalize
> iommu_inclusive_mapping
> 
> On Tue, Jul 31, 2018 at 03:14:47AM -0600, Jan Beulich wrote:
> > >>> On 31.07.18 at 11:05, <roger.pau@xxxxxxxxxx> wrote:
> > > On Tue, Jul 31, 2018 at 02:49:19AM -0600, Jan Beulich wrote:
> > >> >>> On 31.07.18 at 10:37, <Paul.Durrant@xxxxxxxxxx> wrote:
> > >> >>  -----Original Message-----
> > >> >> From: Roger Pau Monne
> > >> >> Sent: 31 July 2018 09:34
> > >> >> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > >> >> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; 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>; Jan
> Beulich
> > >> >> <jbeulich@xxxxxxxx>
> > >> >> Subject: Re: [Xen-devel] [PATCH 2/4] iommu: generalize
> > >> >> iommu_inclusive_mapping
> > >> >>
> > >> >> On Tue, Jul 31, 2018 at 09:27:03AM +0100, Paul Durrant wrote:
> > >> >> > > -----Original Message-----
> > >> >> > > From: Roger Pau Monne
> > >> >> > > Sent: 31 July 2018 09:16
> > >> >> > > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > >> >> > > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; 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>;
> Jan
> > >> >> Beulich
> > >> >> > > <jbeulich@xxxxxxxx>
> > >> >> > > Subject: Re: [Xen-devel] [PATCH 2/4] iommu: generalize
> > >> >> > > iommu_inclusive_mapping
> > >> >> > >
> > >> >> > > On Tue, Jul 31, 2018 at 08:18:36AM +0100, Paul Durrant wrote:
> > >> >> > > > > -----Original Message-----
> > >> >> > > > > From: Xen-devel [mailto:xen-devel-
> bounces@xxxxxxxxxxxxxxxxxxxx]
> > >> >> On
> > >> >> > > Behalf
> > >> >> > > > > Of Roger Pau Monne
> > >> >> > > > > Sent: 27 July 2018 16:32
> > >> >> > > > > To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> > >> >> > > > > 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>; Jan
> > >> >> > > Beulich
> > >> >> > > > > <jbeulich@xxxxxxxx>; Roger Pau Monne
> <roger.pau@xxxxxxxxxx>
> > >> >> > > > > Subject: [Xen-devel] [PATCH 2/4] iommu: generalize
> > >> >> > > > > iommu_inclusive_mapping
> > >> >> > > > >
> > >> >> > > > > Introduce a new iommu=inclusive generic option that
> supersedes
> > >> >> > > > > iommu_inclusive_mapping. This should be a non-functional
> change
> > >> >> on
> > >> >> > > > > Intel hardware, while AMD hardware will gain the same
> functionality
> > >> >> of
> > >> >> > > > > mapping almost everything below the 4GB boundary.
> > >> >> > > > >
> > >> >> > > > > Note that is a noop for ARM hardware.
> > >> >> > > > >
> > >> >> > > > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > >> >> > > > > ---
> > >> >> > > > > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > >> >> > > > > Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> > >> >> > > > > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > >> >> > > > > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > >> >> > > > > Cc: Julien Grall <julien.grall@xxxxxxx>
> > >> >> > > > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > >> >> > > > > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > >> >> > > > > Cc: Tim Deegan <tim@xxxxxxx>
> > >> >> > > > > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > >> >> > > > > Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> > >> >> > > > > ---
> > >> >> > > > >  docs/misc/xen-command-line.markdown   | 14 ++++++
> > >> >> > > > >  xen/drivers/passthrough/arm/iommu.c   |  4 ++
> > >> >> > > > >  xen/drivers/passthrough/iommu.c       |  6 +++
> > >> >> > > > >  xen/drivers/passthrough/vtd/extern.h  |  2 -
> > >> >> > > > >  xen/drivers/passthrough/vtd/iommu.c   |  6 ---
> > >> >> > > > >  xen/drivers/passthrough/vtd/x86/vtd.c | 66 
> > >> >> > > > > +------------------
> ------
> > >> >> > > > >  xen/drivers/passthrough/x86/iommu.c   | 70
> > >> >> > > > > +++++++++++++++++++++++++++
> > >> >> > > > >  xen/include/xen/iommu.h               |  2 +
> > >> >> > > > >  8 files changed, 97 insertions(+), 73 deletions(-)
> > >> >> > > > >
> > >> >> > > > > diff --git a/docs/misc/xen-command-line.markdown
> > >> >> b/docs/misc/xen-
> > >> >> > > > > command-line.markdown
> > >> >> > > > > index 65b4754418..91a8bfc9a6 100644
> > >> >> > > > > --- a/docs/misc/xen-command-line.markdown
> > >> >> > > > > +++ b/docs/misc/xen-command-line.markdown
> > >> >> > > > > @@ -1198,6 +1198,17 @@ detection of systems known to
> misbehave
> > >> >> > > upon
> > >> >> > > > > accesses to that port.
> > >> >> > > > >
> > >> >> > > > >  >> Enable IOMMU debugging code (implies `verbose`).
> > >> >> > > > >
> > >> >> > > > > +> `inclusive`
> > >> >> > > >
> > >> >> > > > This is a dom0 (or hwdom) specific setting so perhaps dom0-
> inclusive?
> > >> >> > > >
> > >> >> > > > Actually the dom0 iommu options are starting to get unwieldy
> as they
> > >> >> are
> > >> >> > > conflated with the general host iommu options so I think it may
> be
> > >> >> > > worthwhile splitting things out into a separate 'dom0-iommu='
> top level
> > >> >> > > parameter at this stage. (My reasons are slightly selfish as I
> intend to
> > >> > add
> > >> >> > > another dom0 iommu option to give it just reserved regions, to
> avoid
> > >> >> > > unnecessary set-up if we know it will be using PV-IOMMU).
> > >> >> > >
> > >> >> > > Mapping just the reserved regions is what I actually do for PVH
> with
> > >> >> > > iommu=inclusive (patch 4/4), so maybe it would make sense to
> speak
> > >> >> about
> > >> >> > > the
> > >> >> > > naming here in order to use the same naming for PV and PVH.
> > >> >> > >
> > >> >> > > TBH I don't really like the dom0- prefix, the command line iommu
> > >> >> > > options either apply to all domains or Dom0 only, having
> > >> >> > > domu-inclusive for example makes no sense IMO.
> > >> >> >
> > >> >> > No, I think there are some options that you may want to apply to
> dom0
> > >> >> only, but these are more like the dom0_mem or dom0_max_vpus
> options.
> > >> >> Particularly, the inclusive option is probably something that is only
> > > desirable
> > >> >> for dom0. Clearly dom0-passthrough and dom0-strict are already
> defined to
> > >> >> relate to dom0 only, and options such as 'reserved' should only be
> specific
> > > on
> > >> >> the command line in relation to dom0 IMO. For other domains such
> an option
> > >> >> should be specified via xl.cfg.
> > >> >>
> > >> >> Yes, we already have a bunch of those, so then I think dom0-
> inclusive
> > >> >> and dom0-reserved would be appropriate?
> > >> >>
> > >> >> dom0-inclusive-mapping or dom0-reserved-mapping seems too
> long.
> > >> >
> > >> > Yes, those names are ok, but I still think it better in the long run 
> > >> > if we
> > >> > have something like:
> > >> >
> > >> > dom0_iommu=[inclusive,][reserved,][strict,][none,][relaxed]
> > >> >
> > >> > where relaxed is the default and 'none' (I think) is equivalent to the
> > >> > current iommu=dom0-passthrough.
> > >>
> > >> Or, along the lines of the other reply just sent, e.g.
> > >>
> > >> dom0=pvh,iommu:inclusive;reserved,shadow
> > >>
> > >> But perhaps the difference between , and ; gets too confusing then.
> > >
> > > So I think we have the following options:
> > >
> > > 1. dom0_iommu=[inclusive,][reserved,][strict,][none,][relaxed]
> >
> > Nit: dom0-iommu= (no underscores in new options)
> >
> > > 2.
> dom0=[pvh,][shadow,][iommu=[inclusive;][reserved;][strict;][none;][relaxe
> d]]
> > > 3. dom0=[pvh,][shadow,][iommu-inclusive,][iommu-reserved,][iommu-
> strict,][iommu-none,][iommu-relaxed]
> > >
> > > I don't have a strong preference between 1 and 3, but I would prefer
> > > to avoid 2 because I think suboptions inside of options it's too
> > > complex IMO.
> >
> > While generally I prefer to limit the number of top level options, in
> > this case I think I'd prefer 1 after all. Or wait - does any pair of the
> > (sub)options actually make sense to be specified?
> 
> Yes, for example you can use strict and inclusive at the same time, I
> think it's something like:
> 
> dom0=[pvh,][shadow,][iommu=[inclusive|reserved;][strict|none|relaxed]]

I think it may be:

dom0=[pvh,][shadow,][iommu=[inclusive|reserved|none;][strict|relaxed]]

where 'none' in the first part means the second part is moot. (Not sure how to 
express that cleanly).

  Paul

> 
> > Isn't it rather a
> > choice of five than an enumeration of up to 5? In which case I'd
> > still prefer 2 (as then there's no need for a second separator
> > beside comma), the more that we have at least one example with
> > such sub-options (cpufreq).
> 
> OK, I can do the nested iommu option inside of dom0 if that's the
> preference.
> 
> Thanks, Roger.

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