On 11/03/2017 10:03 AM, David Herrmann wrote: > Hi > > On Tue, Oct 31, 2017 at 7:40 PM, Marc-André Lureau > <marcandre.lur...@redhat.com> wrote: >> Implements memfd sealing, similar to shmem: >> - WRITE: deny fallocate(PUNCH_HOLE). mmap() write is denied in >> memfd_add_seals(). write() doesn't exist for hugetlbfs. >> - SHRINK: added similar check as shmem_setattr() >> - GROW: added similar check as shmem_setattr() & shmem_fallocate() >> >> Except write() operation that doesn't exist with hugetlbfs, that >> should make sealing as close as it can be to shmem support. > > SEAL, SHRINK, and GROW look fine to me. > > Regarding WRITE
The commit message may not be clear. However, hugetlbfs does not support the write system call (or aio). The only way to modify contents of a hugetlbfs file is via mmap or hole punch/truncate. So, we do not really need to worry about those special (a)io cases for hugetlbfs. -- Mike Kravetz > you need to make sure there are no page references > left around. For instance, on shmem any process might trigger the > kernel to GUP mapped shmem pages for asynchronous IO, then unmap the > file and request F_SEAL_WRITE. In this case the seal must be rejected > *iff* the pages are still pinned. shmem does this by requiring the > page-refcounts to be 0. Preferably there would be some better > infrastructure that tells us whether someone operates on those pages, > but this does not exist right now. See shmem_wait_for_pins() for > details. > > I have little knowledge on how hugetlbs integrate with the page-cache > and radix-tree, hence I'd prefer if someone can explicitly ACK that > shmem_wait_for_pins() is suitable for hugetlbfs. > > Otherwise, this series looks good to me (minus the #ifdef mess..). > > Thanks > David > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majord...@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=ilto:"d...@kvack.org"> em...@kvack.org </a> >
