Messages in this thread | | | Date | Fri, 1 Apr 2022 08:52:12 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown() |
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On Fri, Apr 01, 2022 at 02:20:23PM +0800, Yi Liu wrote: > > > On 2022/3/29 19:42, Jason Gunthorpe wrote: > > On Tue, Mar 29, 2022 at 08:42:13AM +0000, Tian, Kevin wrote: > > > > > btw I'm not sure whether this is what SVA requires. IIRC the problem with > > > SVA is because PASID TLP prefix is not counted in PCI packet routing thus > > > a DMA target address with PASID might be treated as P2P if the address > > > falls into the MMIO BAR of other devices in the group. This is why the > > > original code needs to strictly apply SVA in a group containing a single > > > device, instead of a group attached by a single driver, unless we want to > > > reserve those MMIO ranges in CPU VA space. > > > > I think it is not such a good idea to mix up group with this test > > > > Here you want to say that all TLPs from the RID route to the host > > bridge - ie ACS is on/etc. This is subtly different from a group with > > a single device. Specifically it is an immutable property of the > > fabric and doesn't change after hot plug events. > > so the group size can be immutable for specific topology. right? I think for > non-multi-function devices plugged behind an PCIE bridge which has enabled > ACS, such devices should have their own groups. Under such topology the > group size should be 1 constantly. May just enable SVA for such devices.
Like I said, you should stop thinking about group size.
You need to know that 100% of TLPs translate through the IOMMU to enable SVA, nothing less will do, and that property has nothing to do with group size.
> > ie if we have a singleton group that doesn't have ACS and someone > > hotplugs in another device on a bridge, then our SVA is completely > > broken and we get data corruption. > > I think this may be a device plugged in a PCIE-to-PCI bridge, and then > hotplug a device to this bridge. The group size is variable. right? Per my > understanding, maybe such a bridge cannot support PASID Prefix at all, hence > no SVA support for such devices.
Any PCIE-to-PCIE bridge will do, don't ned to involve legacy PCI here to have hotplug problems.
Jason
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