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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 3DFABC04A6B for ; Tue, 7 May 2019 02:23:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A0CE206BF for ; Tue, 7 May 2019 02:23:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726236AbfEGCXh (ORCPT ); Mon, 6 May 2019 22:23:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41082 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726145AbfEGCXg (ORCPT ); Mon, 6 May 2019 22:23:36 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F155D81127; Tue, 7 May 2019 02:23:35 +0000 (UTC) Received: from hp-dl380pg8-02.lab.eng.pek2.redhat.com (hp-dl380pg8-02.lab.eng.pek2.redhat.com [10.73.8.12]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5C87160BEC; Tue, 7 May 2019 02:23:30 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Christoph Hellwig , James Bottomley , Andrea Arcangeli Subject: [PATCH RFC] vhost: don't use kmap() to log dirty pages Date: Mon, 6 May 2019 22:23:29 -0400 Message-Id: <1557195809-12373-1-git-send-email-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 07 May 2019 02:23:36 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Vhost log dirty pages directly to a userspace bitmap through GUP and kmap_atomic() since kernel doesn't have a set_bit_to_user() helper. This will cause issues for the arch that has virtually tagged caches. The way to fix is to keep using userspace virtual address. Fortunately, futex has a cmpxchg to userspace memory helper futex_atomic_cmpxchg_inatomic(). So switch to use it to exchange the userspace bitmap with zero, set the bit and then write it back through put_user(). Note: there're archs (few non popular ones) that don't implement futex helper, we can't log dirty pages. We can fix them on top or simply disable LOG_ALL features of vhost. Cc: Christoph Hellwig Cc: James Bottomley Cc: Andrea Arcangeli Fixes: 3a4d5c94e9593 ("vhost_net: a kernel-level virtio server") Signed-off-by: Jason Wang --- drivers/vhost/vhost.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 351af88..9c94c41 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -31,6 +31,7 @@ #include #include #include +#include #include "vhost.h" @@ -1692,25 +1693,27 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) } EXPORT_SYMBOL_GPL(vhost_dev_ioctl); -/* TODO: This is really inefficient. We need something like get_user() - * (instruction directly accesses the data, with an exception table entry - * returning -EFAULT). See Documentation/x86/exception-tables.txt. - */ -static int set_bit_to_user(int nr, void __user *addr) +static int set_bit_to_user(int nr, u32 __user *addr) { unsigned long log = (unsigned long)addr; struct page *page; - void *base; - int bit = nr + (log % PAGE_SIZE) * 8; + u32 old_log; int r; r = get_user_pages_fast(log, 1, 1, &page); if (r < 0) return r; BUG_ON(r != 1); - base = kmap_atomic(page); - set_bit(bit, base); - kunmap_atomic(base); + + r = futex_atomic_cmpxchg_inatomic(&old_log, addr, 0, 0); + if (r < 0) + return r; + + old_log |= 1 << nr; + r = put_user(old_log, addr); + if (r < 0) + return r; + set_page_dirty_lock(page); put_page(page); return 0; @@ -1727,8 +1730,8 @@ static int log_write(void __user *log_base, write_length += write_address % VHOST_PAGE_SIZE; for (;;) { u64 base = (u64)(unsigned long)log_base; - u64 log = base + write_page / 8; - int bit = write_page % 8; + u64 log = base + write_page / 32; + int bit = write_page % 32; if ((u64)(unsigned long)log != log) return -EFAULT; r = set_bit_to_user(bit, (void __user *)(unsigned long)log); -- 1.8.3.1