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Message-ID: <aa326283-468f-6c40-4c47-de7cf7cc5994@redhat.com> Date: Wed, 3 May 2023 16:31:36 +0200 From: David Hildenbrand <david@...hat.com> To: Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org> Cc: Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>, Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>, Leon Romanovsky <leon@...nel.org>, Christian Benvenuti <benve@...co.com>, Nelson Escobar <neescoba@...co.com>, Bernard Metzler <bmt@...ich.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, Bjorn Topel <bjorn@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Christian Brauner <brauner@...nel.org>, Richard Cochran <richardcochran@...il.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org, netdev@...r.kernel.org, bpf@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>, Jason Gunthorpe <jgg@...dia.com>, John Hubbard <jhubbard@...dia.com>, Jan Kara <jack@...e.cz>, "Kirill A . Shutemov" <kirill@...temov.name>, Pavel Begunkov <asml.silence@...il.com>, Mika Penttila <mpenttil@...hat.com>, Dave Chinner <david@...morbit.com>, Theodore Ts'o <tytso@....edu>, Peter Xu <peterx@...hat.com>, Matthew Rosato <mjrosato@...ux.ibm.com>, "Paul E . McKenney" <paulmck@...nel.org>, Christian Borntraeger <borntraeger@...ux.ibm.com> Subject: Re: [PATCH v8 1/3] mm/mmap: separate writenotify and dirty tracking logic On 03.05.23 00:51, Lorenzo Stoakes wrote: > vma_wants_writenotify() is specifically intended for setting PTE page table > flags, accounting for existing page table flag state and whether the > filesystem performs dirty tracking. > > Separate out the notions of dirty tracking and PTE write notify checking in > order that we can invoke the dirty tracking check from elsewhere. > > Note that this change introduces a very small duplicate check of the > separated out vm_ops_needs_writenotify() and vma_is_shared_writable() > functions. This is necessary to avoid making vma_needs_dirty_tracking() > needlessly complicated (e.g. passing flags or having it assume checks were > already performed). This is small enough that it doesn't seem too > egregious. > > We check to ensure the mapping is shared writable, as any GUP caller will > be safe - MAP_PRIVATE mappings will be CoW'd and read-only file-backed > shared mappings are not permitted access, even with FOLL_FORCE. > > Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com> > Reviewed-by: John Hubbard <jhubbard@...dia.com> > Reviewed-by: Mika Penttilä <mpenttil@...hat.com> > Reviewed-by: Jan Kara <jack@...e.cz> > Reviewed-by: Jason Gunthorpe <jgg@...dia.com> > --- > include/linux/mm.h | 1 + > mm/mmap.c | 53 ++++++++++++++++++++++++++++++++++------------ > 2 files changed, 41 insertions(+), 13 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 27ce77080c79..7b1d4e7393ef 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2422,6 +2422,7 @@ extern unsigned long move_page_tables(struct vm_area_struct *vma, > #define MM_CP_UFFD_WP_ALL (MM_CP_UFFD_WP | \ > MM_CP_UFFD_WP_RESOLVE) > > +bool vma_needs_dirty_tracking(struct vm_area_struct *vma); > int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot); > static inline bool vma_wants_manual_pte_write_upgrade(struct vm_area_struct *vma) > { > diff --git a/mm/mmap.c b/mm/mmap.c > index 5522130ae606..fa7442e44cc2 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1475,6 +1475,42 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg) > } > #endif /* __ARCH_WANT_SYS_OLD_MMAP */ > > +/* Do VMA operations imply write notify is required? */ Nit: comment is superfluous, this is already self-documenting code. > +static bool vm_ops_needs_writenotify(const struct vm_operations_struct *vm_ops) > +{ > + return vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite); > +} > + > +/* Is this VMA shared and writable? */ Nit: dito > +static bool vma_is_shared_writable(struct vm_area_struct *vma) > +{ > + return (vma->vm_flags & (VM_WRITE | VM_SHARED)) == > + (VM_WRITE | VM_SHARED); > +} > + > +/* > + * Does this VMA require the underlying folios to have their dirty state > + * tracked? > + */ Nit: dito > +bool vma_needs_dirty_tracking(struct vm_area_struct *vma) > +{ > + /* Only shared, writable VMAs require dirty tracking. */ > + if (!vma_is_shared_writable(vma)) > + return false; > + > + /* Does the filesystem need to be notified? */ > + if (vm_ops_needs_writenotify(vma->vm_ops)) > + return true; > + > + /* Specialty mapping? */ > + if (vma->vm_flags & VM_PFNMAP) > + return false; > + > + /* Can the mapping track the dirty pages? */ > + return vma->vm_file && vma->vm_file->f_mapping && > + mapping_can_writeback(vma->vm_file->f_mapping); > +} > + > /* > * Some shared mappings will want the pages marked read-only > * to track write events. If so, we'll downgrade vm_page_prot > @@ -1483,21 +1519,18 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg) > */ > int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot) > { > - vm_flags_t vm_flags = vma->vm_flags; > - const struct vm_operations_struct *vm_ops = vma->vm_ops; > - > /* If it was private or non-writable, the write bit is already clear */ > - if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED))) > + if (!vma_is_shared_writable(vma)) > return 0; > > /* The backer wishes to know when pages are first written to? */ > - if (vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite)) > + if (vm_ops_needs_writenotify(vma->vm_ops)) > return 1; > > /* The open routine did something to the protections that pgprot_modify > * won't preserve? */ > if (pgprot_val(vm_page_prot) != > - pgprot_val(vm_pgprot_modify(vm_page_prot, vm_flags))) > + pgprot_val(vm_pgprot_modify(vm_page_prot, vma->vm_flags))) > return 0; > > /* > @@ -1511,13 +1544,7 @@ int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot) > if (userfaultfd_wp(vma)) > return 1; > > - /* Specialty mapping? */ > - if (vm_flags & VM_PFNMAP) > - return 0; > - > - /* Can the mapping track the dirty pages? */ > - return vma->vm_file && vma->vm_file->f_mapping && > - mapping_can_writeback(vma->vm_file->f_mapping); > + return vma_needs_dirty_tracking(vma); > } > > /* We now have duplicate vma_is_shared_writable() and vm_ops_needs_writenotify() checks ... Maybe move the VM_PFNMAP and "/* Can the mapping track the dirty pages? */" checks into a separate helper and call that from both, vma_wants_writenotify() and vma_needs_dirty_tracking() ? In any case Acked-by: David Hildenbrand <david@...hat.com> -- Thanks, David / dhildenb
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