From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D35EC2D0E0 for ; Tue, 8 Sep 2020 06:20:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 473FA207DE for ; Tue, 8 Sep 2020 06:20:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728911AbgIHGUI (ORCPT ); Tue, 8 Sep 2020 02:20:08 -0400 Received: from verein.lst.de ([213.95.11.211]:51486 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726787AbgIHGUH (ORCPT ); Tue, 8 Sep 2020 02:20:07 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 15E9468AFE; Tue, 8 Sep 2020 08:20:03 +0200 (CEST) Date: Tue, 8 Sep 2020 08:20:02 +0200 From: Christoph Hellwig To: Arnd Bergmann Cc: Christoph Hellwig , Russell King , Alexander Viro , kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linus.walleij@linaro.org, Russell King , Christian Brauner , Andrew Morton , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 5/9] ARM: oabi-compat: rework epoll_wait/epoll_pwait emulation Message-ID: <20200908062002.GD13930@lst.de> References: <20200907153701.2981205-1-arnd@arndb.de> <20200907153701.2981205-6-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200907153701.2981205-6-arnd@arndb.de> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Sep 07, 2020 at 05:36:46PM +0200, Arnd Bergmann wrote: > The epoll_wait() system call wrapper is one of the remaining users of > the set_fs() infrasturcture for Arm. Changing it to not require set_fs() > is rather complex unfortunately. > > The approach I'm taking here is to allow architectures to override > the code that copies the output to user space, and let the oabi-compat > implementation check whether it is getting called from an EABI or OABI > system call based on the thread_info->syscall value. > > The in_oabi_syscall() check here mirrors the in_compat_syscall() and > in_x32_syscall() helpers for 32-bit compat implementations on other > architectures. > > Overall, the amount of code goes down, at least with the newly added > sys_oabi_epoll_pwait() helper getting removed again. The downside > is added complexity in the source code for the native implementation. > There should be no difference in runtime performance except for Arm > kernels with CONFIG_OABI_COMPAT enabled that now have to go through > an external function call to check which of the two variants to use. > > Signed-off-by: Arnd Bergmann > --- > arch/arm/include/asm/syscall.h | 11 +++++ > arch/arm/kernel/sys_oabi-compat.c | 72 +++++++------------------------ > arch/arm/tools/syscall.tbl | 4 +- > fs/eventpoll.c | 5 +-- > include/linux/eventpoll.h | 16 +++++++ > 5 files changed, 46 insertions(+), 62 deletions(-) > > diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h > index ff6cc365eaf7..0d8afceeefd9 100644 > --- a/arch/arm/include/asm/syscall.h > +++ b/arch/arm/include/asm/syscall.h > @@ -28,6 +28,17 @@ static inline int syscall_get_nr(struct task_struct *task, > return task_thread_info(task)->syscall; > } > > +static inline bool __in_oabi_syscall(struct task_struct *task) > +{ > + return IS_ENABLED(CONFIG_OABI_COMPAT) && > + (task_thread_info(task)->syscall & __NR_OABI_SYSCALL_BASE); > +} > + > +static inline bool in_oabi_syscall(void) > +{ > + return __in_oabi_syscall(current); > +} > + > static inline void syscall_rollback(struct task_struct *task, > struct pt_regs *regs) > { > diff --git a/arch/arm/kernel/sys_oabi-compat.c b/arch/arm/kernel/sys_oabi-compat.c > index 2ce3e8c6ca91..abf1153c5315 100644 > --- a/arch/arm/kernel/sys_oabi-compat.c > +++ b/arch/arm/kernel/sys_oabi-compat.c > @@ -83,6 +83,8 @@ > #include > #include > > +#include > + > struct oldabi_stat64 { > unsigned long long st_dev; > unsigned int __pad1; > @@ -264,68 +266,24 @@ asmlinkage long sys_oabi_epoll_ctl(int epfd, int op, int fd, > return do_epoll_ctl(epfd, op, fd, &kernel, false); > } > > -static long do_oabi_epoll_wait(int epfd, struct oabi_epoll_event __user *events, > - int maxevents, int timeout) > +struct epoll_event __user * > +epoll_put_uevent(__poll_t revents, __u64 data, struct epoll_event __user *uevent) > { > + if (in_oabi_syscall()) { > + struct oabi_epoll_event *oevent = (void __user *)uevent; > > + if (__put_user(revents, &oevent->events) || > + __put_user(data, &oevent->data)) > + return NULL; > > + return (void __user *)uevent+1; > + } I wonder if we'd be better off doing the in_oabi_syscall() branch in the common code. E.g. rename in_oabi_syscall to in_legacy_syscall and stub it out for all other architectures. Then just do if (in_oabi_syscall() legacy_syscall_foo_bit(); else normal_syscall_foo_bit(); in common code, where so far only arm provides legacy_syscall_foo_bit(). Tons of long lines again in this patch..