Messages in this thread | | | Date | Mon, 11 May 2015 12:26:18 +1000 | From | Alexey Kardashevskiy <> | Subject | Re: [PATCH kernel v9 31/32] vfio: powerpc/spapr: Support multiple groups in one container if possible |
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On 05/05/2015 09:50 PM, David Gibson wrote: > 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 <aik@ozlabs.ru> >>>>>> [aw: for the vfio related changes] >>>>>> Acked-by: Alex Williamson <alex.williamson@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.
True, it does contradict, I do not know why he said what he said :)
-- Alexey
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