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Tue, 18 Oct 2022 14:51:33 +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 3/5] iommu/s390: Use RCU to allow concurrent domain_list iteration Date: Tue, 18 Oct 2022 16:51:30 +0200 Message-Id: <20221018145132.998866-4-schnelle@linux.ibm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20221018145132.998866-1-schnelle@linux.ibm.com> References: <20221018145132.998866-1-schnelle@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 7hRy3bXDF6ctmnw4xCQcCRPUXE74SKq9 X-Proofpoint-ORIG-GUID: 7hRy3bXDF6ctmnw4xCQcCRPUXE74SKq9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-10-18_04,2022-10-18_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 spamscore=0 priorityscore=1501 mlxlogscore=999 lowpriorityscore=0 clxscore=1015 mlxscore=0 impostorscore=0 adultscore=0 suspectscore=0 phishscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2209130000 definitions=main-2210180083 X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747037659788217527?= X-GMAIL-MSGID: =?utf-8?q?1747037659788217527?= 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 --- arch/s390/include/asm/pci.h | 1 + arch/s390/pci/pci.c | 2 +- drivers/iommu/s390-iommu.c | 31 ++++++++++++++++--------------- 3 files changed, 18 insertions(+), 16 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; 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); } int zpci_report_error(struct pci_dev *pdev, diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c index a4c2e9bc6d83..4e90987be387 100644 --- a/drivers/iommu/s390-iommu.c +++ b/drivers/iommu/s390-iommu.c @@ -10,6 +10,8 @@ #include #include #include +#include +#include #include static const struct iommu_ops s390_iommu_ops; @@ -61,7 +63,7 @@ static struct iommu_domain *s390_domain_alloc(unsigned domain_type) 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); return &s390_domain->domain; } @@ -70,7 +72,9 @@ static void s390_domain_free(struct iommu_domain *domain) { struct s390_domain *s390_domain = to_s390_domain(domain); + rcu_read_lock(); WARN_ON(!list_empty(&s390_domain->devices)); + rcu_read_unlock(); dma_cleanup_tables(s390_domain->dma_table); kfree(s390_domain); } @@ -84,7 +88,7 @@ static void __s390_iommu_detach_device(struct zpci_dev *zdev) return; 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); zpci_unregister_ioat(zdev, 0); @@ -127,7 +131,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain, zdev->s390_domain = s390_domain; 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); return 0; @@ -203,17 +207,16 @@ static void s390_iommu_flush_iotlb_all(struct iommu_domain *domain) { struct s390_domain *s390_domain = to_s390_domain(domain); struct zpci_dev *zdev; - unsigned long flags; int rc; - 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) { rc = zpci_refresh_trans((u64)zdev->fh << 32, zdev->start_dma, zdev->end_dma - zdev->start_dma + 1); if (rc) break; } - spin_unlock_irqrestore(&s390_domain->list_lock, flags); + rcu_read_unlock(); } static void s390_iommu_iotlb_sync(struct iommu_domain *domain, @@ -222,21 +225,20 @@ static void s390_iommu_iotlb_sync(struct iommu_domain *domain, struct s390_domain *s390_domain = to_s390_domain(domain); size_t size = gather->end - gather->start + 1; struct zpci_dev *zdev; - unsigned long flags; int rc; /* If gather was never added to there is nothing to flush */ if (gather->start == ULONG_MAX) return; - 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) { rc = zpci_refresh_trans((u64)zdev->fh << 32, gather->start, size); if (rc) break; } - spin_unlock_irqrestore(&s390_domain->list_lock, flags); + rcu_read_unlock(); } static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain, @@ -244,11 +246,10 @@ static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain, { struct s390_domain *s390_domain = to_s390_domain(domain); struct zpci_dev *zdev; - unsigned long flags; int rc; - 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; rc = zpci_refresh_trans((u64)zdev->fh << 32, @@ -256,7 +257,7 @@ static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain, if (rc) break; } - spin_unlock_irqrestore(&s390_domain->list_lock, flags); + rcu_read_unlock(); } static int s390_iommu_update_trans(struct s390_domain *s390_domain,