> From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> > Sent: Wednesday, September 22, 2021 9:45 PM > > On Sun, Sep 19, 2021 at 02:38:39PM +0800, Liu Yi L wrote: > > This patch adds IOASID allocation/free interface per iommufd. When > > allocating an IOASID, userspace is expected to specify the type and > > format information for the target I/O page table. > > > > This RFC supports only one type > (IOMMU_IOASID_TYPE_KERNEL_TYPE1V2), > > implying a kernel-managed I/O page table with vfio type1v2 mapping > > semantics. For this type the user should specify the addr_width of > > the I/O address space and whether the I/O page table is created in > > an iommu enfore_snoop format. enforce_snoop must be true at this > point, > > as the false setting requires additional contract with KVM on handling > > WBINVD emulation, which can be added later. > > > > Userspace is expected to call IOMMU_CHECK_EXTENSION (see next patch) > > for what formats can be specified when allocating an IOASID. > > > > Open: > > - Devices on PPC platform currently use a different iommu driver in vfio. > > Per previous discussion they can also use vfio type1v2 as long as there > > is a way to claim a specific iova range from a system-wide address space. > > Is this the reason for passing addr_width to IOASID_ALLOC? I didn't get > what it's used for or why it's mandatory. But for PPC it sounds like it > should be an address range instead of an upper limit? yes, as this open described, it may need to be a range. But not sure if PPC requires multiple ranges or just one range. Perhaps, David may guide there. Regards, Yi Liu > Thanks, > Jean > > > This requirement doesn't sound PPC specific, as addr_width for pci > devices > > can be also represented by a range [0, 2^addr_width-1]. This RFC hasn't > > adopted this design yet. We hope to have formal alignment in v1 > discussion > > and then decide how to incorporate it in v2. > > > > - Currently ioasid term has already been used in the kernel > (drivers/iommu/ > > ioasid.c) to represent the hardware I/O address space ID in the wire. It > > covers both PCI PASID (Process Address Space ID) and ARM SSID (Sub- > Stream > > ID). We need find a way to resolve the naming conflict between the > hardware > > ID and software handle. One option is to rename the existing ioasid to be > > pasid or ssid, given their full names still sound generic. Appreciate more > > thoughts on this open!
