Messages in this thread | | | Date | Fri, 1 Apr 2022 14:20:23 +0800 | Subject | Re: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown() | From | Yi Liu <> |
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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.
> 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.
-- Regards, Yi Liu
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