On Tue, 18 Oct 2016 15:06:55 +1100
David Gibson <da...@gibson.dropbear.id.au> wrote:
> On Mon, Oct 17, 2016 at 10:07:36AM -0600, Alex Williamson wrote:
> > On Mon, 17 Oct 2016 18:44:21 +0300
> > "Aviv B.D" <bd.a...@gmail.com> wrote:
> > > From: "Aviv Ben-David" <bd.a...@gmail.com>
> > >
> > > * Advertize Cache Mode capability in iommu cap register.
> > > This capability is controlled by "cache-mode" property of intel-iommu
> > > device.
> > > To enable this option call QEMU with "-device
> > > intel-iommu,cache-mode=true".
> > >
> > > * On page cache invalidation in intel vIOMMU, check if the domain belong
> > > to
> > > registered notifier, and notify accordingly.
> > >
> > > Currently this patch still doesn't enabling VFIO devices support with
> > > vIOMMU
> > > present. Current problems:
> > > * vfio_iommu_map_notify is not aware about memory range belong to
> > > specific
> > > VFIOGuestIOMMU.
> > Could you elaborate on why this is an issue?
> > > * memory_region_iommu_replay hangs QEMU on start up while it itterate
> > > over
> > > 64bit address space. Commenting out the call to this function enables
> > > workable VFIO device while vIOMMU present.
> > This has been discussed previously, it would be incorrect for vfio not
> > to call the replay function. The solution is to add an iommu driver
> > callback to efficiently walk the mappings within a MemoryRegion.
> Right, replay is a bit of a hack. There are a couple of other
> approaches that might be adequate without a new callback:
> - Make the VFIOGuestIOMMU aware of the guest address range mapped
> by the vIOMMU. Intel currently advertises that as a full 64-bit
> address space, but I bet that's not actually true in practice.
> - Have the IOMMU MR advertise a (minimum) page size for vIOMMU
> mappings. That may let you stpe through the range with greater
Hmm, VT-d supports at least a 39-bit address width and always supports
a minimum 4k page size, so yes that does reduce us from 2^52 steps down
to 2^27, but it's still absurd to walk through the raw address space.
It does however seem correct to create the MemoryRegion with a width
that actually matches the IOMMU capability, but I don't think that's a
sufficient fix by itself. Thanks,