On Mon, Oct 28, 2024 at 09:05:44AM -1000, Linus Torvalds wrote: > On Mon, 28 Oct 2024 at 08:57, Lorenzo Stoakes > <lorenzo.stoakes@xxxxxxxxxx> wrote: > > > > So likely hook on your mapping changes flags to set VM_MTE | VM_MTE_ALLOWED and > > expects this to be checked after (ugh). > > Gaah. Yes. mm/shmem.c: shmem_mmap() does > > /* arm64 - allow memory tagging on RAM-based files */ > vm_flags_set(vma, VM_MTE_ALLOWED); > > and while I found the equivalent hack for the VM_SPARC_ADI case, I > hadn't noticed that MTE thing. > > How very annoying. > > So the arch_validate_flags() case does need to be done after the ->mmap() call. > > How about just finalizing everything, and then doing a regular > munmap() afterwards and returning an error (all still holding the mmap > semaphore, of course). > > That still avoids the whole "partially completed mmap" case. > > Linus Yeah I was thinking the same... just bite the bullet, go through the whole damn process and revert if arch_validate_flags() chokes. It also removes the ugly #ifdef CONFIG_SPARC64 hack... This will litearlly only be applicable for these two cases and (hopefully) most of the time you'd not fail it. I mean by then it'll be added into the rmap and such but nothing will be populated yet and we shouldn't be able to fault as vma_start_write() should have incremented the vma lock seqnum. Any issues from the RCU visibility stuff Liam? Any security problems Jann...? It'd suck to have to bring back a partial complete case. Though I do note we handle errors from mmap_file() ok so we could still potentially handle that there, but would sort of semi-undo some of the point of the series.
