From nobody Tue Apr 7 19:06:59 2026 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 CA272C433FE for ; Wed, 9 Nov 2022 14:29:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231504AbiKIO3d (ORCPT ); Wed, 9 Nov 2022 09:29:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231343AbiKIO30 (ORCPT ); Wed, 9 Nov 2022 09:29:26 -0500 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8793418384; Wed, 9 Nov 2022 06:29:25 -0800 (PST) Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.17.1.5/8.17.1.5) with ESMTP id 2A9DxYLZ006660; Wed, 9 Nov 2022 14:29:12 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding; s=pp1; bh=izBFDgbVKHNBefeE4boPFsbeLvNsC62xJH5EVEQLiiA=; b=QhMXisSfxp57kiOxT9hu41X9u4QUzFLS8mc9nNPI1kXijWBwfeOvTjhTDQtt/zls5Z4E TJV6nRrDTEWrquu4YYYwf88g86aM2I8r+iJmyI9I5SySf9HliOwJ1J9N481U4/bPorv/ LFqhDsSvWAscGebIbP12Aac8sZSxSxmu+rCw+wnsCKjPNfsa+vqzoimCUphj4ILsIAni q/98kV98s0/C/EVEOKEpcAxK6n8lp7fNIRlylVpmEtmz6f7zMPBt9OeK68r8zeyd1ubQ 0J7KrLGholQJnM6O0W06Y6nJmiyVkSBNPmI77tuIvDHlnYo2Eh+W5yWGokBSD9d3FLdY 5Q== Received: from ppma05fra.de.ibm.com (6c.4a.5195.ip4.static.sl-reverse.com [149.81.74.108]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3krdjprye2-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 09 Nov 2022 14:29:12 +0000 Received: from pps.filterd (ppma05fra.de.ibm.com [127.0.0.1]) by ppma05fra.de.ibm.com (8.16.1.2/8.16.1.2) with SMTP id 2A9EJtsV021709; Wed, 9 Nov 2022 14:29:09 GMT Received: from b06cxnps3074.portsmouth.uk.ibm.com (d06relay09.portsmouth.uk.ibm.com [9.149.109.194]) by ppma05fra.de.ibm.com with ESMTP id 3krcbr03jv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 09 Nov 2022 14:29:09 +0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 2A9ET6jO38470044 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 9 Nov 2022 14:29:06 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 19E1EA404D; Wed, 9 Nov 2022 14:29:06 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A2CD4A4040; Wed, 9 Nov 2022 14:29:05 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.152.85.9]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 9 Nov 2022 14:29:05 +0000 (GMT) From: Niklas Schnelle To: Matthew Rosato , iommu@lists.linux.dev, Joerg Roedel , Will Deacon , Robin Murphy , Jason Gunthorpe Cc: Gerd Bayer , Pierre Morel , linux-s390@vger.kernel.org, borntraeger@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, gerald.schaefer@linux.ibm.com, agordeev@linux.ibm.com, svens@linux.ibm.com, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/5] iommu/s390: Use RCU to allow concurrent domain_list iteration Date: Wed, 9 Nov 2022 15:29:01 +0100 Message-Id: <20221109142903.4080275-4-schnelle@linux.ibm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20221109142903.4080275-1-schnelle@linux.ibm.com> References: <20221109142903.4080275-1-schnelle@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: q_F5OMFiaz7D4I5FizMLr-E7pL5dVz2x X-Proofpoint-GUID: q_F5OMFiaz7D4I5FizMLr-E7pL5dVz2x X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-11-09_06,2022-11-09_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 malwarescore=0 adultscore=0 spamscore=0 mlxlogscore=999 suspectscore=0 priorityscore=1501 mlxscore=0 bulkscore=0 phishscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2211090107 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The s390_domain->devices list is only added to when new devices are attached but is iterated through in read-only fashion for every mapping operation as well as for I/O TLB flushes and thus in performance critical code causing contention on the s390_domain->list_lock. Fortunately such a read-mostly linked list is a standard use case for RCU. This change closely follows the example fpr RCU protected list given in Documentation/RCU/listRCU.rst. Signed-off-by: Niklas Schnelle --- v1->v2: - Free domain tables via call_rcu() (Jason) arch/s390/include/asm/pci.h | 1 + arch/s390/pci/pci.c | 2 +- drivers/iommu/s390-iommu.c | 44 +++++++++++++++++++++++-------------- 3 files changed, 29 insertions(+), 18 deletions(-) diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h index 07361e2fd8c5..e4c3e4e04d30 100644 --- a/arch/s390/include/asm/pci.h +++ b/arch/s390/include/asm/pci.h @@ -119,6 +119,7 @@ struct zpci_dev { struct list_head entry; /* list of all zpci_devices, needed for hotplug,= etc. */ struct list_head iommu_list; struct kref kref; + struct rcu_head rcu; struct hotplug_slot hotplug_slot; =20 enum zpci_state state; diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c index a703dcd94a68..ef38b1514c77 100644 --- a/arch/s390/pci/pci.c +++ b/arch/s390/pci/pci.c @@ -996,7 +996,7 @@ void zpci_release_device(struct kref *kref) break; } zpci_dbg(3, "rem fid:%x\n", zdev->fid); - kfree(zdev); + kfree_rcu(zdev, rcu); } =20 int zpci_report_error(struct pci_dev *pdev, diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c index 9771bce86e94..cf5dcbcea4e0 100644 --- a/drivers/iommu/s390-iommu.c +++ b/drivers/iommu/s390-iommu.c @@ -10,6 +10,8 @@ #include #include #include +#include +#include #include =20 static const struct iommu_ops s390_iommu_ops; @@ -20,6 +22,7 @@ struct s390_domain { unsigned long *dma_table; spinlock_t dma_table_lock; spinlock_t list_lock; + struct rcu_head rcu; }; =20 static struct s390_domain *to_s390_domain(struct iommu_domain *dom) @@ -61,18 +64,28 @@ static struct iommu_domain *s390_domain_alloc(unsigned = domain_type) =20 spin_lock_init(&s390_domain->dma_table_lock); spin_lock_init(&s390_domain->list_lock); - INIT_LIST_HEAD(&s390_domain->devices); + INIT_LIST_HEAD_RCU(&s390_domain->devices); =20 return &s390_domain->domain; } =20 +static void s390_iommu_rcu_free_domain(struct rcu_head *head) +{ + struct s390_domain *s390_domain =3D container_of(head, struct s390_domain= , rcu); + + dma_cleanup_tables(s390_domain->dma_table); + kfree(s390_domain); +} + static void s390_domain_free(struct iommu_domain *domain) { struct s390_domain *s390_domain =3D to_s390_domain(domain); =20 + rcu_read_lock(); WARN_ON(!list_empty(&s390_domain->devices)); - dma_cleanup_tables(s390_domain->dma_table); - kfree(s390_domain); + rcu_read_unlock(); + + call_rcu(&s390_domain->rcu, s390_iommu_rcu_free_domain); } =20 static void __s390_iommu_detach_device(struct zpci_dev *zdev) @@ -84,7 +97,7 @@ static void __s390_iommu_detach_device(struct zpci_dev *z= dev) return; =20 spin_lock_irqsave(&s390_domain->list_lock, flags); - list_del_init(&zdev->iommu_list); + list_del_rcu(&zdev->iommu_list); spin_unlock_irqrestore(&s390_domain->list_lock, flags); =20 zpci_unregister_ioat(zdev, 0); @@ -127,7 +140,7 @@ static int s390_iommu_attach_device(struct iommu_domain= *domain, zdev->s390_domain =3D s390_domain; =20 spin_lock_irqsave(&s390_domain->list_lock, flags); - list_add(&zdev->iommu_list, &s390_domain->devices); + list_add_rcu(&zdev->iommu_list, &s390_domain->devices); spin_unlock_irqrestore(&s390_domain->list_lock, flags); =20 return 0; @@ -203,14 +216,13 @@ static void s390_iommu_flush_iotlb_all(struct iommu_d= omain *domain) { struct s390_domain *s390_domain =3D to_s390_domain(domain); struct zpci_dev *zdev; - unsigned long flags; =20 - spin_lock_irqsave(&s390_domain->list_lock, flags); - list_for_each_entry(zdev, &s390_domain->devices, iommu_list) { + rcu_read_lock(); + list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) { zpci_refresh_trans((u64)zdev->fh << 32, zdev->start_dma, zdev->end_dma - zdev->start_dma + 1); } - spin_unlock_irqrestore(&s390_domain->list_lock, flags); + rcu_read_unlock(); } =20 static void s390_iommu_iotlb_sync(struct iommu_domain *domain, @@ -219,18 +231,17 @@ static void s390_iommu_iotlb_sync(struct iommu_domain= *domain, struct s390_domain *s390_domain =3D to_s390_domain(domain); size_t size =3D gather->end - gather->start + 1; struct zpci_dev *zdev; - unsigned long flags; =20 /* If gather was never added to there is nothing to flush */ if (!gather->end) return; =20 - spin_lock_irqsave(&s390_domain->list_lock, flags); - list_for_each_entry(zdev, &s390_domain->devices, iommu_list) { + rcu_read_lock(); + list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) { zpci_refresh_trans((u64)zdev->fh << 32, gather->start, size); } - spin_unlock_irqrestore(&s390_domain->list_lock, flags); + rcu_read_unlock(); } =20 static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain, @@ -238,16 +249,15 @@ static void s390_iommu_iotlb_sync_map(struct iommu_do= main *domain, { struct s390_domain *s390_domain =3D to_s390_domain(domain); struct zpci_dev *zdev; - unsigned long flags; =20 - spin_lock_irqsave(&s390_domain->list_lock, flags); - list_for_each_entry(zdev, &s390_domain->devices, iommu_list) { + rcu_read_lock(); + list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) { if (!zdev->tlb_refresh) continue; zpci_refresh_trans((u64)zdev->fh << 32, iova, size); } - spin_unlock_irqrestore(&s390_domain->list_lock, flags); + rcu_read_unlock(); } =20 static int s390_iommu_update_trans(struct s390_domain *s390_domain, --=20 2.34.1