RE: [RFC v2] /dev/iommu uAPI proposal

Tian, Kevin
2021-07-15T03:55:25Z

> From: Shenming Lu <lushenming@huawei.com>
> Sent: Thursday, July 15, 2021 11:21 AM
>
> On 2021/7/9 15:48, Tian, Kevin wrote:
> > 4.6. I/O page fault
> > +++++++++++++++++++
> >
> > uAPI is TBD. Here is just about the high-level flow from host IOMMU driver
> > to guest IOMMU driver and backwards. This flow assumes that I/O page
> faults
> > are reported via IOMMU interrupts. Some devices report faults via device
> > specific way instead of going through the IOMMU. That usage is not
> covered
> > here:
> >
> > - Host IOMMU driver receives a I/O page fault with raw fault_data {rid,
> > pasid, addr};
> >
> > - Host IOMMU driver identifies the faulting I/O page table according to
> > {rid, pasid} and calls the corresponding fault handler with an opaque
> > object (registered by the handler) and raw fault_data (rid, pasid, addr);
> >
> > - IOASID fault handler identifies the corresponding ioasid and device
> > cookie according to the opaque object, generates an user fault_data
> > (ioasid, cookie, addr) in the fault region, and triggers eventfd to
> > userspace;
> >
>
> Hi, I have some doubts here:
>
> For mdev, it seems that the rid in the raw fault_data is the parent device's,
> then in the vSVA scenario, how can we get to know the mdev(cookie) from
> the
> rid and pasid?
>
> And from this point of view，would it be better to register the mdev
> (iommu_register_device()) with the parent device info?
>

This is what is proposed in this RFC. A successful binding generates a new
iommu_dev object for each vfio device. For mdev this object includes
its parent device, the defPASID marking this mdev, and the cookie
representing it in userspace. Later it is iommu_dev being recorded in
the attaching_data when the mdev is attached to an IOASID:

struct iommu_attach_data *__iommu_device_attach(
struct iommu_dev *dev, u32 ioasid, u32 pasid, int flags);

Then when a fault is reported, the fault handler just needs to figure out
iommu_dev according to {rid, pasid} in the raw fault data.

Thanks
Kevin