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Thu, 03 Aug 2023 10:28:45 -0700 (PDT) MIME-Version: 1.0 References: <20230801220733.1987762-1-surenb@google.com> In-Reply-To: <20230801220733.1987762-1-surenb@google.com> From: Suren Baghdasaryan Date: Thu, 3 Aug 2023 10:28:32 -0700 Message-ID: Subject: Re: [PATCH v2 0/6] make vma locking more obvious To: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org, jannh@google.com, willy@infradead.org, liam.howlett@oracle.com, david@redhat.com, peterx@redhat.com, ldufour@linux.ibm.com, vbabka@suse.cz, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, hannes@cmpxchg.org, dave@stgolabs.net, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: mtwjj413s94bixibfm7syewp1n7b84ga X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: F20D818001B X-HE-Tag: 1691083726-109120 X-HE-Meta: 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 nimoUVtC JCi62x3/iLLTLERr+4lHzzoNI0b8DoD0asW6GTy4yetfrmFYoVQRv8glImKZ4YfIGBQMvTCxwLgEDkBx/592rhcZW1owBHioQS7sYYOKQ6fx92nsyIi7QjojH1b6snviYcraCqlZkmHsTeh6UcOdU64eStHXQ+Czf5s+ZEvzArU/cNXmvdbVPSHQr+PArYgcyoH8PFVgctAogwPl4UtK8Rr9/Ne8v6ZvxygX2mK14lw41LZXivBf+iErhrYvcCTlzsGMqbZN8xejHnzZ/6zZIkFvUjRmxhu4LFyjTwfqfFfeP/KPq4JdecpK/cw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 1, 2023 at 3:07=E2=80=AFPM Suren Baghdasaryan wrote: > > During recent vma locking patch reviews Linus and Jann Horn noted a numbe= r > of issues with vma locking and suggested improvements: > > 1. walk_page_range() does not have ability to write-lock a vma during the > walk when it's done under mmap_write_lock. For example s390_reset_cmma(). > > 2. Vma locking is hidden inside vm_flags modifiers and is hard to follow. > Suggestion is to change vm_flags_reset{_once} to assert that vma is > write-locked and require an explicit locking. > > 3. Same issue with vma_prepare() hiding vma locking. > > 4. In userfaultfd vm_flags are modified after vma->vm_userfaultfd_ctx and > page faults can operate on a context while it's changed. > > 5. do_brk_flags() and __install_special_mapping() not locking a newly > created vma before adding it into the mm. While not strictly a problem, > this is fragile if vma is modified after insertion, as in the > mmap_region() case which was recently fixed. Suggestion is to always lock > a new vma before inserting it and making it visible to page faults. > > 6. vma_assert_write_locked() for CONFIG_PER_VMA_LOCK=3Dn would benefit fr= om > being mmap_assert_write_locked() instead of no-op and then any place whic= h > operates on a vma and calls mmap_assert_write_locked() can be converted > into vma_assert_write_locked(). > > I CC'ed stable only on the first patch because others are cleanups and th= e > bug in userfaultfd does not affect stable (lock_vma_under_rcu prevents > uffds from being handled under vma lock protection). However I would be > happy if the whole series is merged into stable 6.4 since it makes vma > locking more maintainable. > > The patches apply cleanly over Linus' ToT and will conflict when applied > over mm-unstable due to missing [1]. The conflict can be easily resolved > by ignoring conflicting deletions but probably simpler to take [1] into > mm-unstable and avoid later conflict. > > [1] commit 6c21e066f925 ("mm/mempolicy: Take VMA lock before replacing po= licy") > > Changes since v1: > - replace walk_page_range() parameter with mm_walk_ops.walk_lock, > per Linus > - introduced page_walk_lock enum to allow different locking modes > during a walk, per Linus > - added Liam's Reviewed-by v3 is posted at https://lore.kernel.org/all/20230803172652.2849981-1-surenb@google.com/ > > Suren Baghdasaryan (6): > mm: enable page walking API to lock vmas during the walk > mm: for !CONFIG_PER_VMA_LOCK equate write lock assertion for vma and > mmap > mm: replace mmap with vma write lock assertions when operating on a > vma > mm: lock vma explicitly before doing vm_flags_reset and > vm_flags_reset_once > mm: always lock new vma before inserting into vma tree > mm: move vma locking out of vma_prepare > > arch/powerpc/kvm/book3s_hv_uvmem.c | 1 + > arch/powerpc/mm/book3s64/subpage_prot.c | 1 + > arch/riscv/mm/pageattr.c | 1 + > arch/s390/mm/gmap.c | 5 ++++ > drivers/infiniband/hw/hfi1/file_ops.c | 1 + > fs/proc/task_mmu.c | 5 ++++ > fs/userfaultfd.c | 6 +++++ > include/linux/mm.h | 13 ++++++--- > include/linux/pagewalk.h | 11 ++++++++ > mm/damon/vaddr.c | 2 ++ > mm/hmm.c | 1 + > mm/hugetlb.c | 2 +- > mm/khugepaged.c | 5 ++-- > mm/ksm.c | 25 ++++++++++------- > mm/madvise.c | 8 +++--- > mm/memcontrol.c | 2 ++ > mm/memory-failure.c | 1 + > mm/memory.c | 2 +- > mm/mempolicy.c | 22 +++++++++------ > mm/migrate_device.c | 1 + > mm/mincore.c | 1 + > mm/mlock.c | 4 ++- > mm/mmap.c | 29 +++++++++++++------- > mm/mprotect.c | 2 ++ > mm/pagewalk.c | 36 ++++++++++++++++++++++--- > mm/vmscan.c | 1 + > 26 files changed, 146 insertions(+), 42 deletions(-) > > -- > 2.41.0.585.gd2178a4bd4-goog >