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Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment |
Date: |
Sat, 28 May 2016 11:39:36 -0600 |
On Sat, 28 May 2016 16:10:55 +0000
"Aviv B.D." <address@hidden> wrote:
> On Sat, May 28, 2016 at 7:02 PM Alex Williamson <address@hidden>
> wrote:
>
> > On Sat, 28 May 2016 10:52:58 +0000
> > "Aviv B.D." <address@hidden> wrote:
> >
> > > Hi,
> > > Your idea to search the relevent VTDAddressSpace and call it's notifier
> > > will
> > > probably work. Next week I'll try to implement it (for now with the
> > costly
> > > scan
> > > of each context).
> >
> > I think an optimization we can make is to use pci_for_each_bus() and
> > pci_for_each_device() to scan only context entries where devices are
> > present. Then for each context entry, retrieve the DID, if it matches
> > the invalidation domain_id, retrieve the VTDAddressSpace and perform a
> > memory_region_notify_iommu() using VTDAddressSpace.iommu. Still
> > horribly inefficient, but an improvement over walking all context
> > entries and avoids gratuitous callbacks between unrelated drivers in
> > QEMU.
> >
>
> Thanks for the references on how I can do it. :)
>
> >
> > Overall, I have very little faith that this will be the only change
> > required to make this work though. For instance, if a device is added
> > or removed from a domain, where is that accounted for? Ideally this
> > should trigger the region_add/region_del listener callbacks, but I
> > don't see how that works with how VT-d creates a fixed VTDAddressSpace
> > per device, and in fact how our QEMU memory model doesn't allow the
> > address space of a device to be dynamically aliased against other
> > address spaces or really changed at all.
> >
> > > I still not sure if populating the MemoryRegion will suffice for hot plug
> > > vfio
> > > device but i'll try to look into it.
> > >
> > > As far as I understand the memory_region_iommu_replay function, it still
> > > scans
> > > the whole 64bit address space, and therefore may hang the VM for a long
> > > time.
> >
> > Then we need to fix that problem, one option might be to make a replay
> > callback on MemoryRegionIOMMUOps that walks the page tables for a given
> > context entry rather than blindly traversing a 64bit address space. We
> > can't simply ignore the issue by #ifdef'ing out the code. I suspect
> > there's a lot more involved to make VT-d interact properly with a
> > physical device than what's been proposed so far. At every
> > invalidation, we need to figure out what's changed and update the host
> > mappings. We also need better, more dynamic address space management
> > to make the virtual hardware reflect physical hardware when we enable
> > things like passthrough mode or have multiple devices sharing an iommu
> > domain. I think we're just barely scratching the surface here. Thanks,
> >
> > Alex
> >
>
>
> I agree with you regarding hotplug, therefore I only ifdef this code out
> and didn't
> delete it. With the call to memory_region_iommu_replay QEMU hangs on startup
> with a very long loop that prevent any device assignment with vIOMMU
> enabled.
>
> I'm hoping not to enlarge the scope of this patch to include hotplug device
> assignment
> with iommu enabled.
It's not just hotplug, any case where an existing domain can be applied
to a device. The series is incomplete without such support and I won't
accept any changes into vfio that disables code that's correct in other
contexts. Thanks,
Alex
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, (continued)
[Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Aviv B.D, 2016/05/21
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Alex Williamson, 2016/05/23
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Alex Williamson, 2016/05/26
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Aviv B.D., 2016/05/28
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Alex Williamson, 2016/05/28
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Aviv B.D., 2016/05/28
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment,
Alex Williamson <=
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Aviv B.D., 2016/05/28
- Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and vIOMMU to support device assignment, Alex Williamson, 2016/05/28
[Qemu-devel] [PATCH v3 2/3] IOMMU: change iommu_op->translate's is_write to flags, add support to NO_FAIL flag mode, Aviv B.D, 2016/05/21