> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Monday, May 31, 2021 11:43 PM > > On Mon, May 31, 2021 at 05:37:35PM +0000, Parav Pandit wrote: > > > In that case, can it be a new system call? Why does it have to be under > /dev/ioasid? > > For example few years back such system call mpin() thought was proposed > in [1]. > > Reference counting of the overall pins are required > > So when a pinned pages is incorporated into an IOASID page table in a later > IOCTL it means it cannot be unpinned while the IOASID page table is using it. Ok. but cant it use the same refcount of that mmu uses? > > This is some trick to organize the pinning into groups and then refcount each > group, thus avoiding needing per-page refcounts. Pinned page refcount is already maintained by the mmu without ioasid, isn't it? > > The data structure would be an interval tree of pins in general > > The ioasid itself would have an interval tree of its own mappings, each entry > in this tree would reference count against an element in the above tree > > Then the ioasid's interval tree would be mapped into a page table tree in HW > format. Does it mean in simple use case [1], second level page table copy is maintained in the IOMMU side via map interface? I hope not. It should use the same as what mmu uses, right? [1] one SIOV/ADI device assigned with one PASID and mapped in guest VM > > The redundant storages are needed to keep track of the refencing and the > CPU page table values for later unpinning. > > Jason
