On Wed, Nov 27, 2024 at 1:38 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote: > On Tue, Nov 26, 2024 at 10:30 PM Jann Horn <jannh@xxxxxxxxxx> wrote: > > On Fri, Nov 22, 2024 at 4:41 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote: > > > This type will be used when setting up a new vma in an f_ops->mmap() > > > hook. Using a separate type from VmAreaRef allows us to have a separate > > > set of operations that you are only able to use during the mmap() hook. > > > For example, the VM_MIXEDMAP flag must not be changed after the initial > > > setup that happens during the f_ops->mmap() hook. > > > > > > To avoid setting invalid flag values, the methods for clearing > > > VM_MAYWRITE and similar involve a check of VM_WRITE, and return an error > > > if VM_WRITE is set. Trying to use `try_clear_maywrite` without checking > > > the return value results in a compilation error because the `Result` > > > type is marked #[must_use]. > > > > > > For now, there's only a method for VM_MIXEDMAP and not VM_PFNMAP. When > > > we add a VM_PFNMAP method, we will need some way to prevent you from > > > setting both VM_MIXEDMAP and VM_PFNMAP on the same vma. > > > > > > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> > > > > Thanks, this looks really neat! > > > > Reviewed-by: Jann Horn <jannh@xxxxxxxxxx> > > > > > + /// Set the `VM_IO` flag on this vma. > > > + /// > > > + /// This marks the vma as being a memory-mapped I/O region. > > > > nit: VM_IO isn't really exclusively used for MMIO; the header comment > > says "Memory mapped I/O or similar", while the comment in > > remap_pfn_range_internal() says "VM_IO tells people not to look at > > these pages (accesses can have side effects)". But I don't really have > > a good definition of what VM_IO actually means; so I don't really have > > a concrete suggestion for what do do here. So my comment isn't very > > actionable, I guess it's fine to leave this as-is unless someone > > actually has a good definition... > > I can use this comment? > > This is used for memory mapped IO and similar. The flag tells other > parts of the kernel to not look at the pages. For memory mapped IO > this is useful as accesses to the pages could have side effects. Yeah, sounds reasonable.