Re: [Qemu-devel] [RFC PATCH 06/10] vfio: Allow hotplug of containers onto existing guest IOMMU mappings

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

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On Thu, Sep 17, 2015 at 10:54:24AM -0600, Alex Williamson wrote:
> On Thu, 2015-09-17 at 23:09 +1000, David Gibson wrote:
> > At present the memory listener used by vfio to keep host IOMMU mappings
> > in sync with the guest memory image assumes that if a guest IOMMU
> > appears, then it has no existing mappings.
> > 
> > This may not be true if a VFIO device is hotplugged onto a guest bus
> > which didn't previously include a VFIO device, and which has existing
> > guest IOMMU mappings.
> > 
> > Therefore, use the memory_region_register_iommu_notifier_replay()
> > function in order to fix this case, replaying existing guest IOMMU
> > mappings, bringing the host IOMMU into sync with the guest IOMMU.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/vfio/common.c | 34 +++++++++++++++++++---------------
> >  1 file changed, 19 insertions(+), 15 deletions(-)
> > 
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index daaac48..543c38e 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -312,6 +312,22 @@ out:
> >      rcu_read_unlock();
> >  }
> >  
> > +static hwaddr vfio_container_granularity(VFIOContainer *container)
> > +{
> > +    uint64_t pgsize;
> > +
> > +    assert(container->iommu_data.iova_pgsizes);
> 
> return (hwaddr)1 << (ffsl(container->iommu_data.iova_pgsizes) - 1;

Ah, yes, that should work.  I didn't do it that way mostly because I
tend to confuse myself when I try to remember exactly how ffs
semantics work.

-- 
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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