From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pz0-f185.google.com (mail-pz0-f185.google.com [209.85.222.185]) by ozlabs.org (Postfix) with ESMTP id 8B763B7D27 for ; Tue, 4 May 2010 23:04:42 +1000 (EST) Received: by pzk15 with SMTP id 15so897327pzk.15 for ; Tue, 04 May 2010 06:04:41 -0700 (PDT) Date: Tue, 4 May 2010 22:04:18 +0900 From: Takuya Yoshikawa To: Takuya Yoshikawa Subject: [RFC][PATCH 7/12 not tested yet] PPC: introduce __set_bit() like function for bitmaps in user space Message-Id: <20100504220418.083929bc.takuya.yoshikawa@gmail.com> In-Reply-To: <20100504215645.6448af8f.takuya.yoshikawa@gmail.com> References: <20100504215645.6448af8f.takuya.yoshikawa@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: linux-arch@vger.kernel.org, x86@kernel.org, arnd@arndb.de, kvm@vger.kernel.org, kvm-ia64@vger.kernel.org, fernando@oss.ntt.co.jp, mtosatti@redhat.com, agraf@suse.de, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, yoshikawa.takuya@oss.ntt.co.jp, linuxppc-dev@ozlabs.org, mingo@redhat.com, paulus@samba.org, avi@redhat.com, hpa@zytor.com, tglx@linutronix.de List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , During the work of KVM's dirty page logging optimization, we encountered the need of manipulating bitmaps in user space efficiantly. To achive this, we introduce a uaccess function for setting a bit in user space following Avi's suggestion. KVM is now using dirty bitmaps for live-migration and VGA. Although we need to update them from kernel side, copying them every time for updating the dirty log is a big bottleneck. Especially, we tested that zero-copy bitmap manipulation improves responses of GUI manipulations a lot. We also found one similar need in drivers/vhost/vhost.c in which the author implemented set_bit_to_user() locally using inefficient functions: see TODO at the top of that. Probably, this kind of need would be common for virtualization area. So we introduce a function set_bit_user_non_atomic(). Signed-off-by: Takuya Yoshikawa Signed-off-by: Fernando Luis Vazquez Cao CC: Alexander Graf CC: Benjamin Herrenschmidt CC: Paul Mackerras --- arch/powerpc/include/asm/uaccess.h | 19 +++++++++++++++++++ 1 files changed, 19 insertions(+), 0 deletions(-) diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h index 3a01ce8..f878326 100644 --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h @@ -321,6 +321,25 @@ do { \ __gu_err; \ }) +static inline int set_bit_user_non_atomic(int nr, void __user *addr) +{ + u8 __user *p; + u8 val; + + p = (u8 __user *)((unsigned long)addr + nr / BITS_PER_BYTE); + if (!access_ok(VERIFY_WRITE, p, 1)) + return -EFAULT; + + if (__get_user(val, p)) + return -EFAULT; + + val |= 1U << (nr % BITS_PER_BYTE); + if (__put_user(val, p)) + return -EFAULT; + + return 0; +} + /* more complex routines */ -- 1.7.0.4