On Tue, Apr 21, 2020 at 4:55 PM Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote: > > On Tue, Apr 21, 2020 at 04:33:46PM -0700, Dave Jiang wrote: > > The actual code is independent of the stage 2 driver code submission that adds > > support for SVM, ENQCMD(S), PASID, and shared workqueues. This code series will > > support dedicated workqueue on a guest with no vIOMMU. > > > > A new device type "mdev" is introduced for the idxd driver. This allows the wq > > to be dedicated to the usage of a VFIO mediated device (mdev). Once the work > > queue (wq) is enabled, an uuid generated by the user can be added to the wq > > through the uuid sysfs attribute for the wq. After the association, a mdev can > > be created using this UUID. The mdev driver code will associate the uuid and > > setup the mdev on the driver side. When the create operation is successful, the > > uuid can be passed to qemu. When the guest boots up, it should discover a DSA > > device when doing PCI discovery. > > I'm feeling really skeptical that adding all this PCI config space and > MMIO BAR emulation to the kernel just to cram this into a VFIO > interface is a good idea, that kind of stuff is much safer in > userspace. > > Particularly since vfio is not really needed once a driver is using > the PASID stuff. We already have general code for drivers to use to > attach a PASID to a mm_struct - and using vfio while disabling all the > DMA/iommu config really seems like an abuse. > > A /dev/idxd char dev that mmaps a bar page and links it to a PASID > seems a lot simpler and saner kernel wise. > > > The mdev utilizes Interrupt Message Store or IMS[3] instead of MSIX for > > interrupts for the guest. This preserves MSIX for host usages and also allows a > > significantly larger number of interrupt vectors for guest usage. > > I never did get a reply to my earlier remarks on the IMS patches. > > The concept of a device specific addr/data table format for MSI is not > Intel specific. This should be general code. We have a device that can > use this kind of kernel capability today. This has been my concern reviewing the implementation. IMS needs more than one in-tree user to validate degrees of freedom in the api. I had been missing a second "in-tree user" to validate the scope of the flexibility that was needed.
