On 2021/6/1 20:30, Lu Baolu wrote: > On 2021/6/1 15:15, Shenming Lu wrote: >> On 2021/6/1 13:10, Lu Baolu wrote: >>> Hi Shenming, >>> >>> On 6/1/21 12:31 PM, Shenming Lu wrote: >>>> On 2021/5/27 15:58, Tian, Kevin wrote: >>>>> /dev/ioasid provides an unified interface for managing I/O page tables for >>>>> devices assigned to userspace. Device passthrough frameworks (VFIO, vDPA, >>>>> etc.) are expected to use this interface instead of creating their own logic to >>>>> isolate untrusted device DMAs initiated by userspace. >>>>> >>>>> This proposal describes the uAPI of /dev/ioasid and also sample sequences >>>>> with VFIO as example in typical usages. The driver-facing kernel API provided >>>>> by the iommu layer is still TBD, which can be discussed after consensus is >>>>> made on this uAPI. >>>>> >>>>> It's based on a lengthy discussion starting from here: >>>>> https://lore.kernel.org/linux-iommu/20210330132830.GO2356281@xxxxxxxxxx/ >>>>> >>>>> It ends up to be a long writing due to many things to be summarized and >>>>> non-trivial effort required to connect them into a complete proposal. >>>>> Hope it provides a clean base to converge. >>>>> >>>> [..] >>>> >>>>> /* >>>>> * Page fault report and response >>>>> * >>>>> * This is TBD. Can be added after other parts are cleared up. Likely it >>>>> * will be a ring buffer shared between user/kernel, an eventfd to notify >>>>> * the user and an ioctl to complete the fault. >>>>> * >>>>> * The fault data is per I/O address space, i.e.: IOASID + faulting_addr >>>>> */ >>>> Hi, >>>> >>>> It seems that the ioasid has different usage in different situation, it could >>>> be directly used in the physical routing, or just a virtual handle that indicates >>>> a page table or a vPASID table (such as the GPA address space, in the simple >>>> passthrough case, the DMA input to IOMMU will just contain a Stream ID, no >>>> Substream ID), right? >>>> >>>> And Baolu suggested that since one device might consume multiple page tables, >>>> it's more reasonable to have one fault handler per page table. By this, do we >>>> have to maintain such an ioasid info list in the IOMMU layer? >>> As discussed earlier, the I/O page fault and cache invalidation paths >>> will have "device labels" so that the information could be easily >>> translated and routed. >>> >>> So it's likely the per-device fault handler registering API in iommu >>> core can be kept, but /dev/ioasid will be grown with a layer to >>> translate and propagate I/O page fault information to the right >>> consumers. >> Yeah, having a general preprocessing of the faults in IOASID seems to be >> a doable direction. But since there may be more than one consumer at the >> same time, who is responsible for registering the per-device fault handler? > > The drivers register per page table fault handlers to /dev/ioasid which > will then register itself to iommu core to listen and route the per- > device I/O page faults. This is just a top level thought. Haven't gone > through the details yet. Need to wait and see what /dev/ioasid finally > looks like. OK. And it needs to be confirmed by Jean since we might migrate the code from io-pgfault.c to IOASID... Anyway, finalize /dev/ioasid first. Thanks, Shenming > > Best regards, > baolu > .
