Hi, On 05/16/2018 04:56 PM, Tian, Kevin wrote: >> From: Lu Baolu [mailto:baolu...@linux.intel.com] >> Sent: Wednesday, May 16, 2018 4:01 PM >> >> Hi Joerg, >> >> Thank you for looking at my patches. >> >> On 05/15/2018 10:11 PM, Joerg Roedel wrote: >>> On Fri, May 04, 2018 at 09:41:15AM +0800, Lu Baolu wrote: >>>> PATCH 4~9 implement per domain PASID table. Current per IOMMU >>>> PASID table implementation is insecure in the cases where >>>> multiple devices under one single IOMMU unit support PASID >>>> feature. With per domain PASID table, we can achieve finer >>>> protection and isolation granularity. >>> Hold on, we hat discussions in the past about doing a system-wide pasid >>> space, so that every mm_struct with devices attached gets the same pasid >>> across all devices it is talking to. Reason was that some devices (will) >>> require this to work correctly. This goes into the opposite direction, >>> so I am a bit confused here. Please explain, is this not longer >>> necessary? >> You are right. System-wide pasid space is necessary, hence PATCH >> 1~3 implement it. But PATCH 4~9 don't go into the opposite direction, >> it's designed to address another potential issue. > one thing you may want to highlight is, even with PATCH 4-9 it's > still doing system-wide PASID space allocation. Just PASID table > itself is kept per-device for isolation purpose as you described > below, i.e. each device can access only those PASIDs which are > allocated to itself while the allocation happens system-wide...
Yes, exactly. Best regards, Lu Baolu > >> With system-wide pasid space, we can use a system-wide pasid table, >> or just keep what we have now(per iommu unit pasid table). Both >> system-wide and per iommu unitpasid table mean that two devices >> might share a single pasid table. That will result in an issue. >> >> For an example, device A is assigned to access the memory space of >> process A, and device B is assigned to access the memory space of >> process B. The dma remapping infrastructure looks like: >> >> .------------------. >> .----------------. | | >> | | | | >> .----------------. | Paging structure | >> | PASID X |--| | for Process A | >> .----------------. | | | >> | | --->'------------------' >> .----------------. .----------------. >> | | | PASID Y |--| >> .----------------. .----------------. | >> | Dev_A context |---| | | | .------------------. >> '----------------' | .----------------. | | | >> | | | | | | | | >> '----------------' | .----------------. | | Paging structure | >> | Dev_B context | -->| | | | for Process B | >> '----------------'----->'----------------' | | | >> | | system-wide v-->'------------------' >> .----------------. pasid table >> | | >> '----------------' >> Intel iommu >> context table >> >> >> Since dev_A and dev_B share a pasid table, the side effect is that a flawed >> dev_A might access the memory space of process B (with pasid y). Vice >> versa, >> a flawed dev_B might access memory space of process A (with pasid x). >> >> What PATCH 4~9 do is to remove such possibility by assigning a pasid table >> for each pci device. Hence, the remapping infrastructure looks like: >> >> >> .------------------. >> | | >> .----------------. | | >> | | | Paging structure | >> .----------------. | for Process A | >> | PASID X | | | >> .----------------.----->'------------------' >> | | >> .----------------. >> | | >> .----------------. >> | | >> .----------------. >> .----------------. | | >> | | .----------------. >> .----------------. | | >> | Dev_A context |------>'----------------' >> '----------------' pasid table >> | | for Dev_A >> '----------------' >> | Dev_B context |--> >> '----------------' | .----------------. >> | | | | | .------------------. >> .----------------. | .----------------. | | >> | | | | | | | >> '----------------' | .----------------. | Paging structure | >> Intel iommu | | | | for Process B | >> context table | .----------------. | | >> | | PASID Y |----->'------------------' >> | .----------------. >> | | | >> | .----------------. >> | | | >> | .----------------. >> v--->| | >> '----------------' >> pasid table >> for Dev_B >> >> >> With this, dev_A has no means to access memory of process B and vice >> versa. >> >> Best regards, >> Lu Baolu _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
