Messages in this thread | | | Date | Sun, 25 Jun 2023 14:30:46 +0800 | Subject | Re: [RFC PATCHES 00/17] IOMMUFD: Deliver IO page faults to user space | From | Baolu Lu <> |
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On 2023/5/31 2:50, Nicolin Chen wrote: > Hi Baolu, > > On Tue, May 30, 2023 at 01:37:07PM +0800, Lu Baolu wrote: > >> This series implements the functionality of delivering IO page faults to >> user space through the IOMMUFD framework. The use case is nested >> translation, where modern IOMMU hardware supports two-stage translation >> tables. The second-stage translation table is managed by the host VMM >> while the first-stage translation table is owned by the user space. >> Hence, any IO page fault that occurs on the first-stage page table >> should be delivered to the user space and handled there. The user space >> should respond the page fault handling result to the device top-down >> through the IOMMUFD response uAPI. >> >> User space indicates its capablity of handling IO page faults by setting >> a user HWPT allocation flag IOMMU_HWPT_ALLOC_FLAGS_IOPF_CAPABLE. IOMMUFD >> will then setup its infrastructure for page fault delivery. Together >> with the iopf-capable flag, user space should also provide an eventfd >> where it will listen on any down-top page fault messages. >> >> On a successful return of the allocation of iopf-capable HWPT, a fault >> fd will be returned. User space can open and read fault messages from it >> once the eventfd is signaled. > > I think that, whether the guest has an IOPF capability or not, > the host should always forward any stage-1 fault/error back to > the guest. Yet, the implementation of this series builds with > the IOPF framework that doesn't report IOMMU_FAULT_DMA_UNRECOV. > > And I have my doubt at the using the IOPF framework with that > IOMMU_PAGE_RESP_ASYNC flag: using the IOPF framework is for > its bottom half workqueue, because a page response could take > a long cycle. But adding that flag feels like we don't really > need the bottom half workqueue, i.e. losing the point of using > the IOPF framework, IMHO. > > Combining the two facts above, I wonder if we really need to > go through the IOPF framework; can't we just register a user > fault handler in the iommufd directly upon a valid event_fd?
Agreed. We should avoid workqueue in sva iopf framework. Perhaps we could go ahead with below code? It will be registered to device with iommu_register_device_fault_handler() in IOMMU_DEV_FEAT_IOPF enabling path. Un-registering in the disable path of cause.
static int io_pgfault_handler(struct iommu_fault *fault, void *cookie) { ioasid_t pasid = fault->prm.pasid; struct device *dev = cookie; struct iommu_domain *domain;
if (fault->type != IOMMU_FAULT_PAGE_REQ) return -EOPNOTSUPP;
if (fault->prm.flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID) domain = iommu_get_domain_for_dev_pasid(dev, pasid, 0); else domain = iommu_get_domain_for_dev(dev);
if (!domain || !domain->iopf_handler) return -ENODEV;
if (domain->type == IOMMU_DOMAIN_SVA) return iommu_queue_iopf(fault, cookie);
return domain->iopf_handler(fault, dev, domain->fault_data); }
Best regards, baolu
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