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Wed, 21 Apr 2021 05:50:37 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 7324868BFE; Wed, 21 Apr 2021 07:50:28 +0200 (CEST) Date: Wed, 21 Apr 2021 07:50:28 +0200 From: "hch@lst.de" To: Arnd Bergmann Cc: Vineet Gupta , Matthew Wilcox , "grygorii.strashko@ti.com" , "netdev@vger.kernel.org" , "ilias.apalodimas@linaro.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "mhocko@kernel.org" , "linux-mm@kvack.org" , "mgorman@suse.de" , "brouer@redhat.com" , "mcroce@linux.microsoft.com" , "linux-snps-arc@lists.infradead.org" , "linuxppc-dev@lists.ozlabs.org" , "hch@lst.de" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems Message-ID: <20210421055028.GA28910@lst.de> References: <20210416230724.2519198-1-willy@infradead.org> <20210416230724.2519198-2-willy@infradead.org> <20210417024522.GP2531743@casper.infradead.org> <9f99b0a0-f1c1-f3b0-5f84-3a4bfc711725@synopsys.com> <20210420031029.GI2531743@casper.infradead.org> <8d0fce1c-be7c-1c9b-bf5c-0c531db496ac@synopsys.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210420_225033_241386_8D6A1846 X-CRM114-Status: GOOD ( 13.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Apr 20, 2021 at 11:20:19PM +0200, Arnd Bergmann wrote: > In that case, there should be no problem for you. > > The main issue is with system calls and ioctls that contain a misaligned > struct member like > > struct s { > u32 a; > u64 b; > }; > > Passing this structure by reference from a 32-bit user space application > to a 64-bit kernel with different alignment constraints means that the > kernel has to convert the structure layout. See > compat_ioctl_preallocate() in fs/ioctl.c for one such example. We've also had this problem with some on-disk structures in the past, but hopefully people desining those have learnt the lesson by now. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel