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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CAB25C433EF for ; Fri, 10 Jun 2022 06:05:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346400AbiFJGFq (ORCPT ); Fri, 10 Jun 2022 02:05:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44984 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235636AbiFJGFn (ORCPT ); Fri, 10 Jun 2022 02:05:43 -0400 Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5684D18CE0C for ; Thu, 9 Jun 2022 23:05:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1654841142; x=1686377142; h=message-id:date:mime-version:cc:subject:to:references: from:in-reply-to:content-transfer-encoding; bh=eo+xtNQ4i2z7QGjeoSzqRoqCbvEk7b9xZryoSlqN2EQ=; b=lXxFLEXKndW70aDCt8X8xgjb8cg1ijneEr0ZL2ZXoJ3qXMjL0E+kB3+P dQafBjpGNYjpm1YbkxayiXjcsUCBgfMdf3exgsFgGSK0Ss7otHQrNGRiz gBBGhNeN+hzbF6Eq8XpRKcvxW5Zc4L6HBKVIZzDd0EE0vAogUHImv095F zdLBtVYndrzXhi9sGTSyTzztu4kuPSXfJRpQmWz6fp46z7tYpKIWiAcbs 6bHvutCsLtwFiCTCtyIHYUR1LbOwKBBkaAvv/rAYB6O/xjsRXGsaJyn4Q mNkE402Iowk92PT5BAmCGM3dGElbj255jKvZYGQDAyTIevmKsE7/KhMc6 Q==; X-IronPort-AV: E=McAfee;i="6400,9594,10373"; a="277559610" X-IronPort-AV: E=Sophos;i="5.91,288,1647327600"; d="scan'208";a="277559610" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jun 2022 23:05:42 -0700 X-IronPort-AV: E=Sophos;i="5.91,288,1647327600"; d="scan'208";a="637955004" Received: from chengxu1-mobl2.ccr.corp.intel.com (HELO [10.249.169.148]) ([10.249.169.148]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jun 2022 23:05:39 -0700 Message-ID: <2ada3a4f-3c2a-f46f-4e39-5c60912cc386@linux.intel.com> Date: Fri, 10 Jun 2022 14:05:37 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Cc: baolu.lu@linux.intel.com, Joerg Roedel , Jason Gunthorpe , Robin Murphy , Kevin Tian , Christoph Hellwig , Will Deacon , Joao Martins , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support Content-Language: en-US To: "Raj, Ashok" References: <20220609070811.902868-1-baolu.lu@linux.intel.com> <20220609170644.GA33363@araj-dh-work> From: Baolu Lu In-Reply-To: <20220609170644.GA33363@araj-dh-work> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/6/10 01:06, Raj, Ashok wrote: > On Thu, Jun 09, 2022 at 03:08:10PM +0800, Lu Baolu wrote: >> The IOMMU page tables are updated using iommu_map/unmap() interfaces. >> Currently, there is no mandatory requirement for drivers to use locks >> to ensure concurrent updates to page tables, because it's assumed that >> overlapping IOVA ranges do not have concurrent updates. Therefore the >> IOMMU drivers only need to take care of concurrent updates to level >> page table entries. > > The last part doesn't read well.. > s/updates to level page table entries/ updates to page-table entries at the > same level > >> >> But enabling new features challenges this assumption. For example, the >> hardware assisted dirty page tracking feature requires scanning page >> tables in interfaces other than mapping and unmapping. This might result >> in a use-after-free scenario in which a level page table has been freed >> by the unmap() interface, while another thread is scanning the next level >> page table. >> >> This adds RCU-protected page free support so that the pages are really >> freed and reused after a RCU grace period. Hence, the page tables are >> safe for scanning within a rcu_read_lock critical region. Considering >> that scanning the page table is a rare case, this also adds a domain >> flag and the RCU-protected page free is only used when this flat is set. > > s/flat/flag Above updated. Thank you! >> >> Signed-off-by: Lu Baolu >> --- >> include/linux/iommu.h | 9 +++++++++ >> drivers/iommu/iommu.c | 23 +++++++++++++++++++++++ >> 2 files changed, 32 insertions(+) >> >> diff --git a/include/linux/iommu.h b/include/linux/iommu.h >> index 5e1afe169549..6f68eabb8567 100644 >> --- a/include/linux/iommu.h >> +++ b/include/linux/iommu.h >> @@ -95,6 +95,7 @@ struct iommu_domain { >> void *handler_token; >> struct iommu_domain_geometry geometry; >> struct iommu_dma_cookie *iova_cookie; >> + unsigned long concurrent_traversal:1; > > Does this need to be a bitfield? Even though you are needing just one bit > now, you can probably make have maskbits? > As discussed in another reply, I am about to drop the driver opt-in and wrapper the helper around the iommu_iotlb_gather. > >> }; >> >> static inline bool iommu_is_dma_domain(struct iommu_domain *domain) >> @@ -657,6 +658,12 @@ static inline void dev_iommu_priv_set(struct device *dev, void *priv) >> dev->iommu->priv = priv; >> } >> >> +static inline void domain_set_concurrent_traversal(struct iommu_domain *domain, >> + bool value) >> +{ >> + domain->concurrent_traversal = value; >> +} >> + >> int iommu_probe_device(struct device *dev); >> void iommu_release_device(struct device *dev); >> >> @@ -677,6 +684,8 @@ int iommu_group_claim_dma_owner(struct iommu_group *group, void *owner); >> void iommu_group_release_dma_owner(struct iommu_group *group); >> bool iommu_group_dma_owner_claimed(struct iommu_group *group); >> >> +void iommu_free_pgtbl_pages(struct iommu_domain *domain, >> + struct list_head *pages); >> #else /* CONFIG_IOMMU_API */ >> >> struct iommu_ops {}; >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >> index 847ad47a2dfd..ceeb97ebe3e2 100644 >> --- a/drivers/iommu/iommu.c >> +++ b/drivers/iommu/iommu.c >> @@ -3252,3 +3252,26 @@ bool iommu_group_dma_owner_claimed(struct iommu_group *group) >> return user; >> } >> EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed); >> + >> +static void pgtble_page_free_rcu(struct rcu_head *rcu) > > maybe the names can be consistent? pgtble_ vs pgtbl below. > > vote to drop the 'e' :-) Updated. > >> +{ >> + struct page *page = container_of(rcu, struct page, rcu_head); >> + >> + __free_pages(page, 0); >> +} >> + >> +void iommu_free_pgtbl_pages(struct iommu_domain *domain, >> + struct list_head *pages) >> +{ >> + struct page *page, *next; >> + >> + if (!domain->concurrent_traversal) { >> + put_pages_list(pages); >> + return; >> + } >> + >> + list_for_each_entry_safe(page, next, pages, lru) { >> + list_del(&page->lru); >> + call_rcu(&page->rcu_head, pgtble_page_free_rcu); >> + } >> +} >> -- >> 2.25.1 >> Best regards, baolu