Messages in this thread | | | Subject | Re: [RFC] /dev/ioasid uAPI proposal | From | Lu Baolu <> | Date | Tue, 1 Jun 2021 13:10:34 +0800 |
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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@nvidia.com/ >> >> 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.
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
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