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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 792C4C433E9 for ; Thu, 18 Mar 2021 10:22:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F2F364F40 for ; Thu, 18 Mar 2021 10:22:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229877AbhCRKVs (ORCPT ); Thu, 18 Mar 2021 06:21:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57392 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229558AbhCRKVP (ORCPT ); Thu, 18 Mar 2021 06:21:15 -0400 Received: from theia.8bytes.org (8bytes.org [IPv6:2a01:238:4383:600:38bc:a715:4b6d:a889]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 770A4C06174A for ; Thu, 18 Mar 2021 03:21:15 -0700 (PDT) Received: by theia.8bytes.org (Postfix, from userid 1000) id 084412D8; Thu, 18 Mar 2021 11:21:13 +0100 (CET) Date: Thu, 18 Mar 2021 11:21:12 +0100 From: Joerg Roedel To: Lu Baolu Cc: Will Deacon , Dave Jiang , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] iommu/vt-d: Fix lockdep splat in intel_pasid_get_entry() Message-ID: References: <20210317005834.173503-1-baolu.lu@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210317005834.173503-1-baolu.lu@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 17, 2021 at 08:58:34AM +0800, Lu Baolu wrote: > The pasid_lock is used to synchronize different threads from modifying a > same pasid directory entry at the same time. It causes below lockdep splat. > > [ 83.296538] ======================================================== > [ 83.296538] WARNING: possible irq lock inversion dependency detected > [ 83.296539] 5.12.0-rc3+ #25 Tainted: G W > [ 83.296539] -------------------------------------------------------- > [ 83.296540] bash/780 just changed the state of lock: > [ 83.296540] ffffffff82b29c98 (device_domain_lock){..-.}-{2:2}, at: > iommu_flush_dev_iotlb.part.0+0x32/0x110 > [ 83.296547] but this lock took another, SOFTIRQ-unsafe lock in the past: > [ 83.296547] (pasid_lock){+.+.}-{2:2} > [ 83.296548] > > and interrupts could create inverse lock ordering between them. > > [ 83.296549] other info that might help us debug this: > [ 83.296549] Chain exists of: > device_domain_lock --> &iommu->lock --> pasid_lock > [ 83.296551] Possible interrupt unsafe locking scenario: > > [ 83.296551] CPU0 CPU1 > [ 83.296552] ---- ---- > [ 83.296552] lock(pasid_lock); > [ 83.296553] local_irq_disable(); > [ 83.296553] lock(device_domain_lock); > [ 83.296554] lock(&iommu->lock); > [ 83.296554] > [ 83.296554] lock(device_domain_lock); > [ 83.296555] > *** DEADLOCK *** > > Fix it by replacing the pasid_lock with an atomic exchange operation. > > Reported-and-tested-by: Dave Jiang > Signed-off-by: Lu Baolu > --- > drivers/iommu/intel/pasid.c | 14 ++++++-------- > 1 file changed, 6 insertions(+), 8 deletions(-) > > diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c > index 9fb3d3e80408..1ddcb8295f72 100644 > --- a/drivers/iommu/intel/pasid.c > +++ b/drivers/iommu/intel/pasid.c > @@ -24,7 +24,6 @@ > /* > * Intel IOMMU system wide PASID name space: > */ > -static DEFINE_SPINLOCK(pasid_lock); > u32 intel_pasid_max_id = PASID_MAX; > > int vcmd_alloc_pasid(struct intel_iommu *iommu, u32 *pasid) > @@ -259,19 +258,18 @@ struct pasid_entry *intel_pasid_get_entry(struct device *dev, u32 pasid) > dir_index = pasid >> PASID_PDE_SHIFT; > index = pasid & PASID_PTE_MASK; > > - spin_lock(&pasid_lock); > entries = get_pasid_table_from_pde(&dir[dir_index]); > if (!entries) { > entries = alloc_pgtable_page(info->iommu->node); > - if (!entries) { > - spin_unlock(&pasid_lock); > + if (!entries) > return NULL; > - } > > - WRITE_ONCE(dir[dir_index].val, > - (u64)virt_to_phys(entries) | PASID_PTE_PRESENT); > + if (cmpxchg64(&dir[dir_index].val, 0ULL, > + (u64)virt_to_phys(entries) | PASID_PTE_PRESENT)) { > + free_pgtable_page(entries); > + entries = get_pasid_table_from_pde(&dir[dir_index]); This is racy, someone could have already cleared the pasid-entry again. What you need to do here is to retry the whole path by adding a goto to before the first get_pasid_table_from_pde() call. Btw, what makes sure that the pasid_entry does not go away when it is returned here? Regards, Joerg