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Thu, 7 Dec 2023 02:13:44 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.9.0-alpha0-1178-geeaf0069a7-fm-20231114.001-geeaf0069 MIME-Version: 1.0 Message-Id: <67fab0f1-e326-4ad8-9def-4d2bd5489b33@app.fastmail.com> In-Reply-To: <20231207002759.51418-8-gregory.price@memverge.com> References: <20231207002759.51418-1-gregory.price@memverge.com> <20231207002759.51418-8-gregory.price@memverge.com> Date: Thu, 07 Dec 2023 08:13:22 +0100 From: "Arnd Bergmann" To: "Gregory Price" , linux-mm@kvack.org, jgroves@micron.com, ravis.opensrc@micron.com, sthanneeru@micron.com, emirakhur@micron.com, Hasan.Maruf@amd.com Cc: linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, Linux-Arch , linux-kernel@vger.kernel.org, "Andrew Morton" , "Thomas Gleixner" , "Andy Lutomirski" , "Ingo Molnar" , "Borislav Petkov" , "Dave Hansen" , x86@kernel.org, "H. Peter Anvin" , "Michal Hocko" , "Tejun Heo" , ying.huang@intel.com, "Gregory Price" , "Jonathan Corbet" , rakie.kim@sk.com, hyeongtak.ji@sk.com, honggyu.kim@sk.com, vtavarespetr@micron.com, "Peter Zijlstra" , "Frank van der Linden" Subject: Re: [RFC PATCH 07/11] mm/mempolicy: add userland mempolicy arg structure Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 448BD80008 X-Stat-Signature: 6ay44m1j9cxxb1ds4ya9kw9ho47ebqn3 X-HE-Tag: 1701933227-742230 X-HE-Meta: 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 dlSlE9Sb FtV9MM47HOxNhxV2xW2RxtamA/MsIPk5ti5L1Rc4H2RzDQY2TzCNRsaak/hn+Qhz+Dmu2ZzzlbQUElzZYuae/u80WG+FfsOVHwY5ziUIrOnLa+xbSNGf39kHhuGdRflvDZYx/ZewT0MGdSKsRFHz5g1/F8hh2hDN6LWMYiOx/3H/vhg+q28O7XOi/FgodIGSeQWhgGGJQjoWvedgIivP/y15624sDShPgxVJuk1aOKPEs6jw= 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 Thu, Dec 7, 2023, at 01:27, Gregory Price wrote: > This patch adds the new user-api argument structure intended for > set_mempolicy2 and mbind2. > > struct mpol_args { > /* Basic mempolicy settings */ > unsigned short mode; > unsigned short mode_flags; > unsigned long *pol_nodes; > unsigned long pol_maxnodes; > > /* get_mempolicy2: policy information (e.g. next interleave node) */ > int policy_node; > > /* get_mempolicy2: memory range policy */ > unsigned long addr; > int addr_node; > > /* all operations: policy home node */ > unsigned long home_node; > > /* mbind2: address ranges to apply the policy */ > const struct iovec __user *vec; > size_t vlen; > }; This is not a great structure layout for a system call ABI, mostly because it requires adding a compat syscall handler to be usable from 32-bit tasks. It would be nice if this could be rewritten in a way that uses only fixed-length members (__u16, __u32, __aligned_u64), though that does require the use of u64_to_user_ptr() to replace the pointers and the reverse in userspace. Aside from this, you should avoid holes in the data structure. On 64-bit architectures, the layout above has holes after policy_node and after addr_node. Arnd