On Mon, Dec 23, 2024 at 10:28:32AM +0800, Baolu Lu wrote: > On 12/19/24 13:06, Nicolin Chen wrote: > > On Thu, Dec 19, 2024 at 10:05:53AM +0800, Baolu Lu wrote: > > > On 12/18/24 13:00, Nicolin Chen wrote: > > > > This is a reverse search v.s. iommufd_viommu_find_dev, as drivers may want > > > > to convert a struct device pointer (physical) to its virtual device ID for > > > > an event injection to the user space VM. > > > > > > > > Again, this avoids exposing more core structures to the drivers, than the > > > > iommufd_viommu alone. > > > > > > > > Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx> > > > > --- > > > > include/linux/iommufd.h | 8 ++++++++ > > > > drivers/iommu/iommufd/driver.c | 20 ++++++++++++++++++++ > > > > 2 files changed, 28 insertions(+) > > > > > > > > diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h > > > > index b082676c9e43..ac1f1897d290 100644 > > > > --- a/include/linux/iommufd.h > > > > +++ b/include/linux/iommufd.h > > > > @@ -190,6 +190,8 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx, > > > > enum iommufd_object_type type); > > > > struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu, > > > > unsigned long vdev_id); > > > > +unsigned long iommufd_viommu_get_vdev_id(struct iommufd_viommu *viommu, > > > > + struct device *dev); > > > Hi Nicolin, > > > > > > This series overall looks good to me. But I have a question that might > > > be irrelevant to this series itself. > > > > > > The iommufd provides both IOMMUFD_OBJ_DEVICE and IOMMUFD_OBJ_VDEVICE > > > objects. What is the essential difference between these two from > > > userspace's perspective? > > A quick answer is an IOMMUFD_OBJ_DEVICE being a host physical > > device and an IOMMUFD_OBJ_VDEVICE being an IOMMUFD_OBJ_DEVICE > > related to IOMMUFD_OBJ_VIOMMU. Two of them can be seen in two > > different layers. May refer to this graph: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/ > > Documentation/userspace-api/iommufd.rst?h=v6.13-rc3#n150 > > > > > And, which object ID should the IOMMU device > > > driver provide when reporting other events in the future? > > > > > > Currently, the IOMMUFD uAPI reports IOMMUFD_OBJ_DEVICE in the page > > > fault message, and IOMMUFD_OBJ_VDEVICE (if I understand it correctly) in > > > the vIRQ message. It will be more future-proof if this could be defined > > > clearly. > > A vIRQ is actually reported per-vIOMMU in this design. Although > > in the this series the SMMU driver seems to report a per-device > > vIRQ, it internally converts the vDEVICE to a virtual device ID > > and packs the virtual device ID into a per-vIOMMU event: > > > > +/** > > + * struct iommu_virq_arm_smmuv3 - ARM SMMUv3 Virtual IRQ > > + * (IOMMU_VIRQ_TYPE_ARM_SMMUV3) > > + * @evt: 256-bit ARM SMMUv3 Event record, little-endian. > > + * (Refer to "7.3 Event records" in SMMUv3 HW Spec) > > + * > > + * StreamID field reports a virtual device ID. To receive a virtual IRQ for a > > + * device, a vDEVICE must be allocated via IOMMU_VDEVICE_ALLOC. > > + */ > > +struct iommu_virq_arm_smmuv3 { > > + __aligned_le64 evt[4]; > > }; > > Thanks for the explanation. Maybe I am a bit over-considering here. > > Initially, my understanding is to report a virtual device ID when the > object originates from a vIOMMU, and an iommufd device ID otherwise. > > However, considering page fault scenarios, which are self-contained but > linked to a hardware page table (hwpt), introduces ambiguity. Hwpt can > be created with or without a vIOMMU. This raises the question: should > the page fault message always report the iommufd device ID, or should > the reporting depend on whether the hwpt was created from a vIOMMU? As you mentioned, HWPT itself can report IO page faults regardless of vIOMMU-based or not, i.e. it should just work fine with a HWPT- based model or a vIOMMU-based model. On the other hand, I think vIRQ can be seen as just a supplementary pathway to report non-HWPT faults, e.g. in arm-smmu-v3's interrupt handler, the logic is: if (pri_is_supported && fault_is_iopgfault) report via hwpt->fault; else if (virq_is_registered && fault_is_virq) report via virq; else print an unhandled irq; Thanks Nicolin
