On Fri, May 01, 2015 at 04:05:24PM +1000, Alexey Kardashevskiy wrote: > On 05/01/2015 02:33 PM, David Gibson wrote: > >On Thu, Apr 30, 2015 at 07:33:09PM +1000, Alexey Kardashevskiy wrote: > >>On 04/30/2015 05:22 PM, David Gibson wrote: > >>>On Sat, Apr 25, 2015 at 10:14:55PM +1000, Alexey Kardashevskiy wrote: > >>>>At the moment only one group per container is supported. > >>>>POWER8 CPUs have more flexible design and allows naving 2 TCE tables per > >>>>IOMMU group so we can relax this limitation and support multiple groups > >>>>per container. > >>> > >>>It's not obvious why allowing multiple TCE tables per PE has any > >>>pearing on allowing multiple groups per container. > >> > >> > >>This patchset is a global TCE tables rework (patches 1..30, roughly) with 2 > >>outcomes: > >>1. reusing the same IOMMU table for multiple groups - patch 31; > >>2. allowing dynamic create/remove of IOMMU tables - patch 32. > >> > >>I can remove this one from the patchset and post it separately later but > >>since 1..30 aim to support both 1) and 2), I'd think I better keep them all > >>together (might explain some of changes I do in 1..30). > > > >The combined patchset is fine. My comment is because your commit > >message says that multiple groups are possible *because* 2 TCE tables > >per group are allowed, and it's not at all clear why one follows from > >the other. > > > Ah. That's wrong indeed, I'll fix it. > > > >>>>This adds TCE table descriptors to a container and uses > >>>>iommu_table_group_ops > >>>>to create/set DMA windows on IOMMU groups so the same TCE tables will be > >>>>shared between several IOMMU groups. > >>>> > >>>>Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > >>>>[aw: for the vfio related changes] > >>>>Acked-by: Alex Williamson <alex.william...@redhat.com> > >>>>--- > >>>>Changes: > >>>>v7: > >>>>* updated doc > >>>>--- > >>>> Documentation/vfio.txt | 8 +- > >>>> drivers/vfio/vfio_iommu_spapr_tce.c | 268 > >>>> ++++++++++++++++++++++++++---------- > >>>> 2 files changed, 199 insertions(+), 77 deletions(-) > >>>> > >>>>diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt > >>>>index 94328c8..7dcf2b5 100644 > >>>>--- a/Documentation/vfio.txt > >>>>+++ b/Documentation/vfio.txt > >>>>@@ -289,10 +289,12 @@ PPC64 sPAPR implementation note > >>>> > >>>> This implementation has some specifics: > >>>> > >>>>-1) Only one IOMMU group per container is supported as an IOMMU group > >>>>-represents the minimal entity which isolation can be guaranteed for and > >>>>-groups are allocated statically, one per a Partitionable Endpoint (PE) > >>>>+1) On older systems (POWER7 with P5IOC2/IODA1) only one IOMMU group per > >>>>+container is supported as an IOMMU table is allocated at the boot time, > >>>>+one table per a IOMMU group which is a Partitionable Endpoint (PE) > >>>> (PE is often a PCI domain but not always). > >>> > >>>I thought the more fundamental problem was that different PEs tended > >>>to use disjoint bus address ranges, so even by duplicating put_tce > >>>across PEs you couldn't have a common address space. > >> > >> > >>Sorry, I am not following you here. > >> > >>By duplicating put_tce, I can have multiple IOMMU groups on the same virtual > >>PHB in QEMU, "[PATCH qemu v7 04/14] spapr_pci_vfio: Enable multiple groups > >>per container" does this, the address ranges will the same. > > > >Oh, ok. For some reason I thought that (at least on the older > >machines) the different PEs used different and not easily changeable > >DMA windows in bus addresses space. > > > They do use different tables (which VFIO does not get to remove/create and > uses these old helpers - iommu_take/release_ownership), correct. But all > these windows are mapped at zero on a PE's PCI bus and nothing prevents me > from updating all these tables with the same TCE values when handling > H_PUT_TCE. Yes it is slow but it works (bit more details below).
Um.. I'm pretty sure that contradicts what Ben was saying on the
thread.
> >>What I cannot do on p5ioc2 is programming the same table to multiple
> >>physical PHBs (or I could but it is very different than IODA2 and pretty
> >>ugly and might not always be possible because I would have to allocate these
> >>pages from some common pool and face problems like fragmentation).
> >
> >So allowing multiple groups per container should be possible (at the
> >kernel rather than qemu level) by writing the same value to multiple
> >TCE tables. I guess its not worth doing for just the almost-obsolete
> >IOMMUs though.
>
>
> It is done at QEMU level though. As it works now, QEMU opens a group, walks
> through all existing containers and tries attaching a new group there. If it
> succeeded (x86 always; POWER8 after this patch), a TCE table is shared. If
> it failed, QEMU creates another container, attaches it to the same VFIO/PHB
> address space and attaches a group there.
>
> Then the only thing left is repeating ioctl() in vfio_container_ioctl() for
> every container in the VFIO address space; this is what that QEMU patch does
> (the first version of that patch called ioctl() only for the first container
> in the address space).
>
> From the kernel prospective there are 2 isolated containers; I'd like to
> keep it this way.
>
> btw thanks for the detailed review :)
>
--
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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