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? Thanks, Shenming > > If things evolve in this way, probably the SVA I/O page fault also needs > to be ported to /dev/ioasid. > >> >> Then if we add host IOPF support (for the GPA address space) in the future >> (I have sent a series for this but it aimed for VFIO, I will convert it for >> IOASID later [1] :-)), how could we find the handler for the received fault >> event which only contains a Stream ID... Do we also have to maintain a >> dev(vPASID)->ioasid mapping in the IOMMU layer? >> >> [1] https://lore.kernel.org/patchwork/cover/1410223/ > > Best regards, > baolu > .
