Re: [Xen-devel] [PATCH v3 2/2] VT-d: reconcile iommu_inclusive_mapping and iommu=dom0-strict

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx]
> Sent: 21 June 2018 08:21
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap
> <George.Dunlap@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Jan
> Beulich <jbeulich@xxxxxxxx>; Julien Grall <julien.grall@xxxxxxx>; Konrad
> Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; Stefano Stabellini
> <sstabellini@xxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>
> Subject: RE: [PATCH v3 2/2] VT-d: reconcile iommu_inclusive_mapping and
> iommu=dom0-strict
> 
> > From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
> > Sent: Saturday, June 16, 2018 12:31 AM
> >
> > The documentation for the iommu_inclusive_mapping Xen command line
> > option
> > states:
> >
> > "Use this to work around firmware issues providing incorrect RMRR
> > entries"
> >
> > Unfortunately this workaround does not function correctly if the dom0-
> > strict
> > iommu option is also specified.
> >
> > The documentation goes on to say:
> >
> > "Rather than only mapping RAM pages for IOMMU accesses for Dom0, with
> > this
> >  option all pages up to 4GB, not marked as unusable in the E820 table, will
> >  get a mapping established."
> >
> > This patch modifies the VT-d hardware domain initialization code such that
> > the workaround will continue to function in dom0-strict mode, by mapping
> > all pages not marked as unusable *unless* they are RAM pages not
> > assigned
> > to dom0.
> >
> > NOTE: This patch modifies the test in drivers/passthrough/vtd/iommu.c
> > from
> >       need_iommu() to is_pv_domain() since dom0-strict implies
> > need_iommu()
> >       so we no longer want to gate invocation od vtd_set_hwdom_mapping()
> 
> od->of

Good spot. Can this be fixed up at commit please?

  Paul

> 
> >       on that.
> >       It also exports the iommu_dom0_strict flag so that the implementation
> >       of vtd_set_hwdom_mapping() can test it explicitly. It would be
> >       possible to test need_iommu() instead, but it is more illustrative
> >       to test the original flag rather than one of its side-effects.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > Reviewed-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> 
> Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

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