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Fri, 04 Aug 2023 08:59:41 -0700 (PDT) MIME-Version: 1.0 References: <20230727093637.1262110-1-usama.anjum@collabora.com> <20230727093637.1262110-3-usama.anjum@collabora.com> In-Reply-To: From: Andrei Vagin Date: Fri, 4 Aug 2023 08:59:30 -0700 Message-ID: Subject: Re: [PATCH v26 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs To: =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Cc: Muhammad Usama Anjum , Peter Xu , David Hildenbrand , Andrew Morton , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Mike Rapoport , Nadav Amit , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com, =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C3700120006 X-Stat-Signature: i8gn4x57hwq9etzr7bgf7e7wgxtephwc X-HE-Tag: 1691164782-679627 X-HE-Meta: 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 eqKczw5k 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 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 8:25=E2=80=AFAM Micha=C5=82 Miros=C5=82aw wrote: > > On Thu, 3 Aug 2023 at 17:09, Andrei Vagin wrote: > > On Thu, Jul 27, 2023 at 02:36:34PM +0500, Muhammad Usama Anjum wrote: > [...] > > > + n_pages =3D (*end - addr) / PAGE_SIZE; > > > + if (check_add_overflow(p->found_pages, n_pages, &total_pages) |= | > > > + total_pages > p->arg.max_pages) { > > > > why do we need to use check_add_overflow here? > > > > > + size_t n_too_much =3D total_pages - p->arg.max_pages; > > > > it is unsafe to use total_pages if check_add_overflow returns non-zero. > > Since we're adding unsigned integers, this is well defined even after ove= rflow. The description of check_add_overflow declares that is unsafe: https://elixir.bootlin.com/linux/latest/source/include/linux/overflow.h#L62 It actually doesn't matter, because it should be impossible to overflow total_pages and we can consider not to use check_add_overflow here. > > Best Regards > Micha=C5=82 Miros=C5=82aw