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Tue, 01 Aug 2023 14:46:39 -0700 (PDT) MIME-Version: 1.0 References: <20230731171233.1098105-1-surenb@google.com> <20230731171233.1098105-2-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 1 Aug 2023 14:46:25 -0700 Message-ID: Subject: Re: [PATCH 1/6] mm: enable page walking API to lock vmas during the walk To: Peter Xu Cc: Linus Torvalds , akpm@linux-foundation.org, jannh@google.com, willy@infradead.org, liam.howlett@oracle.com, david@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-Server: rspam08 X-Rspamd-Queue-Id: 94855160009 X-Stat-Signature: 5exuaet4k66ie4zpth6crkrw19d5y8if X-Rspam-User: X-HE-Tag: 1690926400-259139 X-HE-Meta: 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 /ugUe2KJ rSvy2YorvMstqMfryohBCNM1/l6s29OovQUJ6w6V+RucOR5YcUD9XIBaHskZCNVe/iToe5Fgs4uKJCToOGxRxFRZObXeysdGespbNtAmal0d30rVLUT7cQNNMWOgfb05RKHdJ0kDr/sFSlL3dKTXT2gjJpLqCxXRC5zqWuWmps8EQzMSCbDkdi6FJynPl2aV8nWCx4rKPm3/WM2X6JoIQTW967raViSiMjTjEXV5Km7ZUVmEd0SqgEMOXXg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000073, 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 2:34=E2=80=AFPM Peter Xu wrote: > > On Tue, Aug 01, 2023 at 01:28:56PM -0700, Suren Baghdasaryan wrote: > > I have the new patchset ready but I see 3 places where we walk the > > pages after mmap_write_lock() while *I think* we can tolerate > > concurrent page faults (don't need to lock the vmas): > > > > s390_enable_sie() > > break_ksm() > > clear_refs_write() > > This one doesn't look right to be listed - tlb flushing is postponed afte= r > pgtable lock released, so I assume the same issue can happen like fork(): > where we can have race coditions to corrupt data if, e.g., thread A > writting with a writable (unflushed) tlb, alongside with thread B CoWing. Ah, good point. > > It'll indeed be nice to know whether break_ksm() can avoid that lock_vma > parameter across quite a few function jumps. I don't yet see an immediate > issue with this one.. No idea on s390_enable_sie(), but to make it simpl= e > and safe I'd simply leave it with the write vma lock to match the mmap > write lock. Thanks for taking a look, Peter! Ok, let me keep all three of them with vma locking in place to be safe and will post v2 for further discussion. Thanks, Suren. > > Thanks, > > -- > Peter Xu >