Re: [Qemu-devel] [PATCH 3/4] spapr_iommu: Provide a function to switch a TCE table to allowing VFIO

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Sep 30, 2015 at 12:07:39PM +0200, Thomas Huth wrote:
> On 30/09/15 05:48, David Gibson wrote:
> > Because of the way non-VFIO guest IOMMU operations are KVM accelerated, not
> > all TCE tables (guest IOMMU contexts) can support VFIO devices.  Currently,
> > this is decided at creation time.
> > 
> > To support hotplug of VFIO devices, we need to allow a TCE table which
> > previously didn't allow VFIO devices to be switched so that it can.  This
> > patch adds an spapr_tce_set_need_vfio() function to do this, by
> > reallocating the table in userspace if necessary.
> > 
> > Currently this doesn't allow the KVM acceleration to be re-enabled if all
> > the VFIO devices are removed.  That's an optimization for another time.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/ppc/spapr_iommu.c   | 32 ++++++++++++++++++++++++++++++++
> >  include/hw/ppc/spapr.h |  2 ++
> >  2 files changed, 34 insertions(+)
> > 
> > diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
> > index 5166cde..8d60f8b 100644
> > --- a/hw/ppc/spapr_iommu.c
> > +++ b/hw/ppc/spapr_iommu.c
> > @@ -168,6 +168,38 @@ static int spapr_tce_table_realize(DeviceState *dev)
> >      return 0;
> >  }
> >  
> > +void spapr_tce_set_need_vfio(sPAPRTCETable *tcet, bool need_vfio)
> > +{
> > +    size_t table_size = tcet->nb_table * sizeof(uint64_t);
> > +    void *newtable;
> > +
> > +    if (need_vfio == tcet->need_vfio) {
> > +        /* Nothing to do */
> > +        return;
> > +    }
> > +
> > +    if (!need_vfio) {
> > +        /* FIXME: We don't support transition back to KVM accelerated
> > +         * TCEs yet */
> > +        return;
> > +    }
> > +
> > +    tcet->need_vfio = true;
> > +
> > +    if (tcet->fd < 0) {
> > +        /* Table is already in userspace, nothing to be do */
> > +        return;
> > +    }
> > +
> > +    newtable = g_malloc0(table_size);
> 
> Since you immediately fill the whole table with the memcpy below, you do
> not need to zero the memory here, i.e. g_malloc instead of g_malloc0
> should be sufficient.

True, I just used malloc0 out of habit.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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