Re: [Xen-devel] [PATCH] x86/vtd: fix IOMMU share PT destruction path

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 09 October 2018 15:26
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Jan Beulich <JBeulich@xxxxxxxx>; Roger Pau Monne
> <roger.pau@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>
> Subject: Re: [PATCH] x86/vtd: fix IOMMU share PT destruction path
> 
> On Tue, Oct 09, 2018 at 11:42:17AM +0100, Wei Liu wrote:
> > Commit 2916951c1 ("mm / iommu: include need_iommu() test in
> > iommu_use_hap_pt()") included need_iommu() in iommu_use_hap_pt and
> > 91d4eca7add (" mm / iommu: split need_iommu() into has_iommu_pt() and
> > need_iommu_pt_sync()") made things finer grain by spliting need_iommu
> > into three states.
> >
> > The destruction path can't use iommu_use_hap_pt because at the point
> > platform op is called, IOMMU is already switched to disabled state and
> > the shared PT test would always be false.
> >
> > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > ---
> >  xen/drivers/passthrough/vtd/iommu.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/drivers/passthrough/vtd/iommu.c
> b/xen/drivers/passthrough/vtd/iommu.c
> > index f94b522c73..d66d9e8ad0 100644
> > --- a/xen/drivers/passthrough/vtd/iommu.c
> > +++ b/xen/drivers/passthrough/vtd/iommu.c
> > @@ -1752,7 +1752,13 @@ static void iommu_domain_teardown(struct domain
> *d)
> >          xfree(mrmrr);
> >      }
> >
> > -    if ( iommu_use_hap_pt(d) )
> > +    ASSERT(hap_enabled(d));
> 
> This needs to be moved into the predicate below because PV domain can
> enter this path too.
> 
> > +
> > +    /*
> > +     * We can't use iommu_use_hap_pt here because the IOMMU state is
> already
> > +     * changed to IOMMU_STATUS_disabled at this point.
> > +     */
> > +    if ( iommu_hap_pt_share )
> >          return;

I guess the other option is to track whether there is anything to tear down in 
the iommu struct and test that. We have status and need_sync now, but maybe 
that's too simplistic.

  Paul

> >
> >      spin_lock(&hd->arch.mapping_lock);
> > --
> > 2.11.0
> >

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