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Howlett" , Vlastimil Babka , Suren Baghdasaryan , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v2 4/5] mm: make vma cache SLAB_TYPESAFE_BY_RCU Message-ID: References: <20241112194635.444146-1-surenb@google.com> <20241112194635.444146-5-surenb@google.com> <54b8d0b9-a1c7-4c1b-a588-2e5308a977fb@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 7C02112001E X-Stat-Signature: 7k1ikqngg15n39ueqxyo5dou89yid5oc X-Rspam-User: X-HE-Tag: 1731531530-421378 X-HE-Meta: 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 Wbn0Sq+G ej/Gfr3rPpgDGXwHtNLvNdjCWngIo4hPDCmMn1S0kcab4CUjBptac/eVsGLeIIUXqV/PF3FE02otdMNmeuglS+OadK118zJFAuuprrFAaUFMx/3V1t3dbswXo/WybNfpFOQpqNNUx2w7PLG8OBChJ24kyF/nLSlJEUzS5lXwL9+dZ8I8mr7Xxb8kBkKquKFOYljKeDQMEtMCW32E6CsoP5w5FQJA8Q03t6Nwp3iGo+zaj2KBfB9EFss+IjGaUeikBm6qITXFqgusrxuRsIoAHq9ULRg== 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: List-Subscribe: List-Unsubscribe: On Wed, Nov 13, 2024 at 05:44:00PM +0100, Jann Horn wrote: > Something like NULL or (void*)1 is fine with me but please don't do > pointer-to-itself - we shouldn't unnecessarily store a pointer to an > object of one type in a pointer field of an incompatible type, that > increases the risk of creating type confusion issues (both in the > memory corruption sense and in the Spectre sense). I know MM already > has several places where similar stuff can happen (in particular > page->mapping), but here it seems like unnecessary risk to me. Hm? I don't think page->mapping can ever point at page. As far as I know, we have four cases, discriminated by the bottom two bits: 0 - NULL or address_space 1 - anon_vma 2 - movable_ops 3 - ksm_stable_node In fact, we're almost done eliminating page->mapping. Just a few filesystems and device drivers left to go. Would it be halpful if we did: - struct address_space *mapping; + union { + struct address_space *mapping; + unsigned long raw_mapping; + }; and had non-filesystems use raw_mapping and do the masking?