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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E2BAC433EF for ; Thu, 21 Oct 2021 02:26:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64058611CC for ; Thu, 21 Oct 2021 02:26:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230478AbhJUC26 (ORCPT ); Wed, 20 Oct 2021 22:28:58 -0400 Received: from mga12.intel.com ([192.55.52.136]:42356 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229842AbhJUC24 (ORCPT ); Wed, 20 Oct 2021 22:28:56 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10143"; a="209028655" X-IronPort-AV: E=Sophos;i="5.87,168,1631602800"; d="scan'208";a="209028655" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Oct 2021 19:26:41 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.87,168,1631602800"; d="scan'208";a="483985485" Received: from allen-box.sh.intel.com (HELO [10.239.159.118]) ([10.239.159.118]) by orsmga007.jf.intel.com with ESMTP; 20 Oct 2021 19:26:37 -0700 Cc: baolu.lu@linux.intel.com, Sven Peter , iommu@lists.linux-foundation.org, Robin Murphy , Arnd Bergmann , Hector Martin , linux-kernel@vger.kernel.org, Alexander Graf , Mohamed Mediouni , Will Deacon , Alyssa Rosenzweig Subject: Re: [PATCH v3 4/6] iommu: Move IOMMU pagesize check to attach_device To: Marc Zyngier References: <20211019163737.46269-1-sven@svenpeter.dev> <20211019163737.46269-5-sven@svenpeter.dev> <9e25f2c0-d9d3-475d-e973-63be1891f9a5@linux.intel.com> <8735ovdbcv.wl-maz@kernel.org> From: Lu Baolu Message-ID: <6a886030-cbc6-9e92-bf79-77b659da2915@linux.intel.com> Date: Thu, 21 Oct 2021 10:22:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <8735ovdbcv.wl-maz@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/20/21 10:22 PM, Marc Zyngier wrote: > On Wed, 20 Oct 2021 06:21:44 +0100, > Lu Baolu wrote: >> >> On 2021/10/20 0:37, Sven Peter via iommu wrote: >>> The iova allocator is capable of handling any granularity which is a power >>> of two. Remove the much stronger condition that the granularity must be >>> smaller or equal to the CPU page size from a BUG_ON there. >>> Instead, check this condition during __iommu_attach_device and fail >>> gracefully. >>> >>> Signed-off-by: Sven Peter >>> --- >>> drivers/iommu/iommu.c | 35 ++++++++++++++++++++++++++++++++--- >>> drivers/iommu/iova.c | 7 ++++--- >>> include/linux/iommu.h | 5 +++++ >>> 3 files changed, 41 insertions(+), 6 deletions(-) >>> >>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >>> index dd7863e453a5..28896739964b 100644 >>> --- a/drivers/iommu/iommu.c >>> +++ b/drivers/iommu/iommu.c >>> @@ -80,6 +80,8 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus, >>> unsigned type); >>> static int __iommu_attach_device(struct iommu_domain *domain, >>> struct device *dev); >>> +static void __iommu_detach_device(struct iommu_domain *domain, >>> + struct device *dev); >>> static int __iommu_attach_group(struct iommu_domain *domain, >>> struct iommu_group *group); >>> static void __iommu_detach_group(struct iommu_domain *domain, >>> @@ -1974,6 +1976,19 @@ void iommu_domain_free(struct iommu_domain *domain) >>> } >>> EXPORT_SYMBOL_GPL(iommu_domain_free); >>> +static int iommu_check_page_size(struct iommu_domain *domain) >>> +{ >>> + if (!iommu_is_paging_domain(domain)) >>> + return 0; >>> + >>> + if (!(domain->pgsize_bitmap & (PAGE_SIZE | (PAGE_SIZE - 1)))) { >>> + pr_warn("IOMMU pages cannot exactly represent CPU pages.\n"); >>> + return -EFAULT; >>> + } >>> + >>> + return 0; >>> +} >>> + >>> static int __iommu_attach_device(struct iommu_domain *domain, >>> struct device *dev) >>> { >>> @@ -1983,9 +1998,23 @@ static int __iommu_attach_device(struct iommu_domain *domain, >>> return -ENODEV; >>> ret = domain->ops->attach_dev(domain, dev); >>> - if (!ret) >>> - trace_attach_device_to_domain(dev); >>> - return ret; >>> + if (ret) >>> + return ret; >>> + >>> + /* >>> + * Check that CPU pages can be represented by the IOVA granularity. >>> + * This has to be done after ops->attach_dev since many IOMMU drivers >>> + * only limit domain->pgsize_bitmap after having attached the first >>> + * device. >>> + */ >>> + ret = iommu_check_page_size(domain); >>> + if (ret) { >>> + __iommu_detach_device(domain, dev); >>> + return ret; >>> + } >> >> It looks odd. __iommu_attach_device() attaches an I/O page table for a >> device. How does it relate to CPU pages? Why is it a failure case if CPU >> page size is not covered? > > If you allocate a CPU PAGE_SIZE'd region, and point it at a device > that now can DMA to more than what you have allocated because the > IOMMU's own page size is larger, the device has now access to data it > shouldn't see. In my book, that's a pretty bad thing. But even you enforce the CPU page size check here, this problem still exists unless all DMA buffers are PAGE_SIZE aligned and sized, right? Best regards, baolu