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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 35605C1B0D8 for ; Wed, 9 Dec 2020 09:04:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 151D423B75 for ; Wed, 9 Dec 2020 09:04:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728781AbgLIJEW (ORCPT ); Wed, 9 Dec 2020 04:04:22 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:9562 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728740AbgLIJEO (ORCPT ); Wed, 9 Dec 2020 04:04:14 -0500 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4CrWKQ3ZT5zM1q1; Wed, 9 Dec 2020 17:02:50 +0800 (CST) Received: from [127.0.0.1] (10.174.177.9) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.487.0; Wed, 9 Dec 2020 17:03:25 +0800 Subject: Re: [RESEND PATCH v3 2/4] iommu/iova: Avoid double-negatives in magazine helpers To: John Garry , , , CC: , , , References: <1605608734-84416-1-git-send-email-john.garry@huawei.com> <1605608734-84416-3-git-send-email-john.garry@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <7eb70f4b-b050-24ca-f1fa-d8f3c9ddce65@huawei.com> Date: Wed, 9 Dec 2020 17:03:24 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <1605608734-84416-3-git-send-email-john.garry@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.9] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/11/17 18:25, John Garry wrote: > A similar crash to the following could be observed if initial CPU rcache > magazine allocations fail in init_iova_rcaches(): > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 > Mem abort info: > ESR = 0x96000004 > EC = 0x25: DABT (current EL), IL = 32 bits > SET = 0, FnV = 0 > EA = 0, S1PTW = 0 > Data abort info: > ISV = 0, ISS = 0x00000004 > CM = 0, WnR = 0 > [0000000000000000] user address but active_mm is swapper > Internal error: Oops: 96000004 [#1] PREEMPT SMP > Modules linked in: > CPU: 11 PID: 696 Comm: irq/40-hisi_sas Not tainted 5.9.0-rc7-dirty #109 > Hardware name: Huawei D06 /D06, BIOS Hisilicon D06 UEFI RC0 - V1.16.01 03/15/2019 > Call trace: > free_iova_fast+0xfc/0x280 > iommu_dma_free_iova+0x64/0x70 > __iommu_dma_unmap+0x9c/0xf8 > iommu_dma_unmap_sg+0xa8/0xc8 > dma_unmap_sg_attrs+0x28/0x50 > cq_thread_v3_hw+0x2dc/0x528 > irq_thread_fn+0x2c/0xa0 > irq_thread+0x130/0x1e0 > kthread+0x154/0x158 > ret_from_fork+0x10/0x34 > > Code: f9400060 f102001f 54000981 d4210000 (f9400043) > > ---[ end trace 4afcbdfc61b60467 ]--- > > The issue is that expression !iova_magazine_full(NULL) evaluates true; this > falls over in in __iova_rcache_insert() when we attempt to cache a mag > and cpu_rcache->loaded == NULL: > > if (!iova_magazine_full(cpu_rcache->loaded)) { > can_insert = true; > ... > > if (can_insert) > iova_magazine_push(cpu_rcache->loaded, iova_pfn); > > As above, can_insert is evaluated true, which it shouldn't be, and we try > to insert pfns in a NULL mag, which is not safe. > > To avoid this, stop using double-negatives, like !iova_magazine_full() and > !iova_magazine_empty(), and use positive tests, like > iova_magazine_has_space() and iova_magazine_has_pfns(), respectively; these > can safely deal with cpu_rcache->{loaded, prev} = NULL. > > Signed-off-by: John Garry > --- > drivers/iommu/iova.c | 29 +++++++++++++++++------------ > 1 file changed, 17 insertions(+), 12 deletions(-) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index 81b7399dd5e8..1f3f0f8b12e0 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -827,14 +827,18 @@ iova_magazine_free_pfns(struct iova_magazine *mag, struct iova_domain *iovad) > mag->size = 0; > } > > -static bool iova_magazine_full(struct iova_magazine *mag) > +static bool iova_magazine_has_space(struct iova_magazine *mag) > { > - return (mag && mag->size == IOVA_MAG_SIZE); > + if (!mag) > + return false; > + return mag->size < IOVA_MAG_SIZE; > } > > -static bool iova_magazine_empty(struct iova_magazine *mag) > +static bool iova_magazine_has_pfns(struct iova_magazine *mag) > { > - return (!mag || mag->size == 0); > + if (!mag) > + return false; > + return mag->size; > } > > static unsigned long iova_magazine_pop(struct iova_magazine *mag, > @@ -843,7 +847,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag, > int i; > unsigned long pfn; > > - BUG_ON(iova_magazine_empty(mag)); > + BUG_ON(!iova_magazine_has_pfns(mag)); > > /* Only fall back to the rbtree if we have no suitable pfns at all */ > for (i = mag->size - 1; mag->pfns[i] > limit_pfn; i--) > @@ -859,7 +863,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag, > > static void iova_magazine_push(struct iova_magazine *mag, unsigned long pfn) > { > - BUG_ON(iova_magazine_full(mag)); > + BUG_ON(!iova_magazine_has_space(mag)); > > mag->pfns[mag->size++] = pfn; > } > @@ -905,9 +909,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, > cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches); > spin_lock_irqsave(&cpu_rcache->lock, flags); > > - if (!iova_magazine_full(cpu_rcache->loaded)) { > + if (iova_magazine_has_space(cpu_rcache->loaded)) { > can_insert = true; > - } else if (!iova_magazine_full(cpu_rcache->prev)) { > + } else if (iova_magazine_has_space(cpu_rcache->prev)) { > swap(cpu_rcache->prev, cpu_rcache->loaded); > can_insert = true; > } else { > @@ -916,8 +920,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, > if (new_mag) { > spin_lock(&rcache->lock); > if (rcache->depot_size < MAX_GLOBAL_MAGS) { > - rcache->depot[rcache->depot_size++] = > - cpu_rcache->loaded; > + if (cpu_rcache->loaded) Looks like it just needs to change this place. Compiler ensures that mag->size will not be accessed when mag is NULL. static bool iova_magazine_full(struct iova_magazine *mag) { return (mag && mag->size == IOVA_MAG_SIZE); } static bool iova_magazine_empty(struct iova_magazine *mag) { return (!mag || mag->size == 0); } > + rcache->depot[rcache->depot_size++] = > + cpu_rcache->loaded; > } else { > mag_to_free = cpu_rcache->loaded; > } > @@ -968,9 +973,9 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, > cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches); > spin_lock_irqsave(&cpu_rcache->lock, flags); > > - if (!iova_magazine_empty(cpu_rcache->loaded)) { > + if (iova_magazine_has_pfns(cpu_rcache->loaded)) { > has_pfn = true; > - } else if (!iova_magazine_empty(cpu_rcache->prev)) { > + } else if (iova_magazine_has_pfns(cpu_rcache->prev)) { > swap(cpu_rcache->prev, cpu_rcache->loaded); > has_pfn = true; > } else { >