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Fri, 04 Aug 2023 08:30:13 -0700 (PDT) MIME-Version: 1.0 References: <20230803172652.2849981-1-surenb@google.com> In-Reply-To: <20230803172652.2849981-1-surenb@google.com> From: Suren Baghdasaryan Date: Fri, 4 Aug 2023 08:29:57 -0700 Message-ID: Subject: Re: [PATCH v3 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-Rspamd-Queue-Id: 285E020035 X-Rspam-User: X-Stat-Signature: sz1mui3dsxtggkxyxudg3q33ei915y3g X-Rspamd-Server: rspam03 X-HE-Tag: 1691163014-451204 X-HE-Meta: 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 zyUNJX5S Tiv2BKGGAql31IA+Ss8MXxpPEEZcziGX+erkLDMcH/5zAXtargeo+mmlfOe0C5ZBW8ZDWS3WjlX0jzoXaJmtLsoYgrJcYdKn1bEWXJ4nZC8K6MOIWTBf8buy8zRsBejyYSoTOk8jYcsGqmoWJJ+RjJ1d/EaWcFwD4u4H3fZUImf0Coo5FqFqeIqTwY8tZFlevsvxsS7CajWkuCmxKULJ+wd52GWw6NjwGEbqAu1TQqx/12v9cK1ETTuzkiPz0XdymHX4Vj9k+daK4/TltLtIjDA0kxqiK2gPxHkZvNqSXFGUwvD7iLdJGGUEYTw== 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 Thu, Aug 3, 2023 at 10:26=E2=80=AFAM 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 v2: > - removed vma locking from hfi1_file_mmap(), per Linus > - moved vma locking out of dup_anon_vma(), per Liam > - added Liam's Reviewed-by v4 is posted at https://lore.kernel.org/all/20230804152724.3090321-1-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 and dup_anon_vma > > 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 ++++ > 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 | 32 ++++++++++++++-------- > mm/mprotect.c | 2 ++ > mm/pagewalk.c | 36 ++++++++++++++++++++++--- > mm/vmscan.c | 1 + > 25 files changed, 147 insertions(+), 43 deletions(-) > > -- > 2.41.0.585.gd2178a4bd4-goog >