On Wed, Jun 25, 2025 at 03:26:44PM -0400, Peter Xu wrote: > On Wed, Jun 25, 2025 at 03:41:54PM -0300, Jason Gunthorpe wrote: > > On Wed, Jun 25, 2025 at 01:12:11PM -0400, Peter Xu wrote: > > > > > After I read the two use cases, I mostly agree. Just one trivial thing to > > > mention, it may not be direct map but vmap() (see io_region_init_ptr()). > > > > If it is vmapped then this is all silly, you should vmap and mmmap > > using the same cache colouring and, AFAIK, pgoff is how this works for > > purely userspace. > > > > Once vmap'd it should determine the cache colour and set the pgoff > > properly, then everything should already work no? > > I don't yet see how to set the pgoff. Here pgoff is passed from the > userspace, which follows io_uring's definition (per io_uring_mmap). That's too bad So you have to do it the other way and pass the pgoff to the vmap so the vmap ends up with the same colouring as a user VMa holding the same pages.. > So if we want the new API to be proposed here, and make VFIO use it first > (while consider it to be applicable to all existing MMU users at least, > which I checked all of them so far now), I'd think this proper: > > int (*mmap_va_hint)(struct file *file, unsigned long *pgoff, size_t len); > > The changes comparing to previous: > > (1) merged pgoff and *phys_pgoff parameters into one unsigned long, so > the hook can adjust the pgoff for the va allocator to be used. The > adjustment will not be visible to future mmap() when VMA is created. It seems functional, but the above is better, IMHO. > (2) I renamed it to mmap_va_hint(), because *pgoff will be able to be > updated, so it's not only about ordering, but "order" and "pgoff > adjustment" hints that the core mm will use when calculating the VA. Where does order come back though? Returns order? It seems viable Jason
