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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 E6BDCC04AB1 for ; Mon, 13 May 2019 05:27:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B9AE4208C3 for ; Mon, 13 May 2019 05:27:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727539AbfEMF1z (ORCPT ); Mon, 13 May 2019 01:27:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57516 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725970AbfEMF1z (ORCPT ); Mon, 13 May 2019 01:27:55 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 13DF085362; Mon, 13 May 2019 05:27:54 +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 367401822B; Mon, 13 May 2019 05:27:47 +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 , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Darren Hart Subject: [PATCH net] vhost: don't use kmap() to log dirty pages Date: Mon, 13 May 2019 01:27:45 -0400 Message-Id: <1557725265-63525-1-git-send-email-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 13 May 2019 05:27:54 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 arch_futex_atomic_op_inuser() which could be used for setting a bit to user. Note there're several cases that futex helper can fail e.g a page fault or the arch that doesn't have the support. For those cases, a simplified get_user()/put_user() pair protected by a global mutex is provided as a fallback. The fallback may lead false positive that userspace may see more dirty pages. Cc: Christoph Hellwig Cc: James Bottomley Cc: Andrea Arcangeli Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Darren Hart Fixes: 3a4d5c94e9593 ("vhost_net: a kernel-level virtio server") Signed-off-by: Jason Wang --- Changes from RFC V2: - drop GUP and provide get_user()/put_user() fallbacks - round down log_base Changes from RFC V1: - switch to use arch_futex_atomic_op_inuser() --- drivers/vhost/vhost.c | 54 ++++++++++++++++++++++++++++----------------------- 1 file changed, 30 insertions(+), 24 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 351af88..7fa05ba 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -31,6 +31,7 @@ #include #include #include +#include #include "vhost.h" @@ -43,6 +44,8 @@ MODULE_PARM_DESC(max_iotlb_entries, "Maximum number of iotlb entries. (default: 2048)"); +static DEFINE_MUTEX(vhost_log_lock); + enum { VHOST_MEMORY_F_LOG = 0x1, }; @@ -1692,28 +1695,31 @@ 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; 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); - set_page_dirty_lock(page); - put_page(page); + r = arch_futex_atomic_op_inuser(FUTEX_OP_OR, 1 << nr, &old, addr); + if (r) { + /* Fallback through get_user()/put_user(), this may + * lead false positive that userspace may see more + * dirty pages. A mutex is used to synchronize log + * access between vhost threads. + */ + mutex_lock(&vhost_log_lock); + r = get_user(old, addr); + if (r) + goto err; + r = put_user(old | 1 << nr, addr); + if (r) + goto err; + mutex_unlock(&vhost_log_lock); + } return 0; +err: + mutex_unlock(&vhost_log_lock); + return r; } static int log_write(void __user *log_base, @@ -1725,13 +1731,13 @@ static int log_write(void __user *log_base, if (!write_length) return 0; write_length += write_address % VHOST_PAGE_SIZE; + log_base = (void __user *)((u64)log_base & ~0x3ULL); + write_page += ((u64)log_base & 0x3ULL) * 8; for (;;) { - u64 base = (u64)(unsigned long)log_base; - u64 log = base + write_page / 8; - int bit = write_page % 8; - if ((u64)(unsigned long)log != log) - return -EFAULT; - r = set_bit_to_user(bit, (void __user *)(unsigned long)log); + u32 __user *log = (u32 __user *)log_base + write_page / 32; + int bit = write_page % 32; + + r = set_bit_to_user(bit, log); if (r < 0) return r; if (write_length <= VHOST_PAGE_SIZE) -- 1.8.3.1