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Tue, 01 Aug 2023 15:14:08 -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 15:13:56 -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-Queue-Id: 00FC9100005 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: yi7yybay8dhi46nntgikdsextbmydeiy X-HE-Tag: 1690928049-89151 X-HE-Meta: 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 EVNxsVbv Y2UVHfauID1Ka44tR+ZTTCkWbd+rKisBVsEx6/d6I2whK0lobEKSckGwQe2F+hnbv2Gd4Dpyz5DBIzMNxJXslJkmgoN/JrrQePjcHrXkkJPtfjBHUfcJu65vMEPz3EEWKYkWx4Tt1Vaaj83dvLrzRP3Cjnmq8NmzUyFIpbzqU9MW25atRxTz0Jg2OSjkW7BDN1cdeJl6sEXptog+CIkgfZmaiPJqotxq6GA5+r4o5+GQC5Nqm+nxTdoPrNbXYBvOkzlqWPbKosq4WUjW2m8y49uxXqgVusXckOspd5AmwajgpPXZrNs4PCyNml7yhs2pu2zf0RWPhr0AxzH8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000039, 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 2:46=E2=80=AFPM Suren Baghdasaryan wrote: > > 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 af= ter > > 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 CoWin= g. > > Ah, good point. > > > > > It'll indeed be nice to know whether break_ksm() can avoid that lock_vm= a > > parameter across quite a few function jumps. I don't yet see an immedia= te > > issue with this one.. No idea on s390_enable_sie(), but to make it sim= ple > > 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. v2 posted at https://lore.kernel.org/all/20230801220733.1987762-1-surenb@go= ogle.com/ > Thanks, > Suren. > > > > > Thanks, > > > > -- > > Peter Xu > >