Hi All, This patch series converts s390's PCI support from its platform specific DMA API implementation in arch/s390/pci/pci_dma.c to the common DMA IOMMU layer. The conversion itself is done in patches 3-4 with patch 2 providing the final necessary IOMMU driver improvement to handle s390's special IOTLB flush out-of-resource indication in virtualized environments. Patches 1-2 may be applied independently. The conversion itself only touches the s390 IOMMU driver and s390 arch code moving over remaining functions from the s390 DMA API implementation. No changes to common code are necessary. After patch 4 the basic conversion is done and on our partitioning machine hypervisor LPAR performance matches or exceeds the existing code. When running under z/VM or KVM however, performance plummets to about half of the existing code due to a much higher rate of IOTLB flushes for unmapped pages. Due to the hypervisors use of IOTLB flushes to synchronize their shadow tables these are very expensive and minimizing them is key for regaining the performance loss. To this end patches 5-6 add a new, single queue, IOTLB flushing scheme as an alternative to the existing per-CPU flush queues. Introducing an alternative scheme was also suggested by Robin Murphy[1]. In the previous RFC of this conversion Robin suggested reusing more of the existing queuing logic which I incorporated since v2. The single queue mode is introduced in patch 5 together with a new dma_iommu_options struct and tune_dma_iommu callback in IOMMU ops which allows IOMMU drivers to switch to a single flush queue. Then patch 6 enables variable queue sizes using power of 2 queue sizes and shift/mask to keep performance as close to the existing code as possible. The variable queue size and a variable timeout are added to the dma_iommu_options struct and utilized by s390 in the z/VM and KVM guest cases. As it is implemented in common code the single queue IOTLB flushing scheme can of course be used by other platforms with expensive IOTLB flushes. Particularly virtio-iommu may be a candidate. In a previous version I verified that the new scheme does work on my x86_64 Ryzen workstation by locally modifying iommu_subsys_init() to default to the single queue mode and verifying its use via "/sys/.../iommu_group/type". I did not find problems with an AMD GPU, Intel NIC (with SR-IOV and KVM pass-through), NVMes or any on board peripherals. This code is also available in the b4/dma_iommu topic branch of my git.kernel.org repository[3] with tags the version sent. NOTE: Due to the large drop in performance I think we should not merge the DMA API conversion (patch 4) until we have a more suited IOVA flushing scheme with similar improvements as the proposed changes. Best regards, Niklas [0] https://lore.kernel.org/linux-iommu/20221109142903.4080275-1-schnelle@xxxxxxxxxxxxx/ [1] https://lore.kernel.org/linux-iommu/3e402947-61f9-b7e8-1414-fde006257b6f@xxxxxxx/ [2] https://lore.kernel.org/linux-iommu/a8e778da-7b41-a6ba-83c3-c366a426c3da@xxxxxxx/ [3] https://git.kernel.org/pub/scm/linux/kernel/git/niks/linux.git/ --- Changes in v9: - Rebased on v6.4-rc2 - Re-ordered iommu_group_store_type() to allow passing the device to iommu_dma_init_fq() - Link to v8: https://lore.kernel.org/r/20230310-dma_iommu-v8-0-2347dfbed7af@xxxxxxxxxxxxx --- Niklas Schnelle (6): s390/ism: Set DMA coherent mask iommu: Allow .iotlb_sync_map to fail and handle s390's -ENOMEM return s390/pci: prepare is_passed_through() for dma-iommu s390/pci: Use dma-iommu layer iommu/dma: Allow a single FQ in addition to per-CPU FQs iommu/dma: Make flush queue sizes and timeout driver configurable Documentation/admin-guide/kernel-parameters.txt | 9 +- arch/s390/include/asm/pci.h | 7 - arch/s390/include/asm/pci_clp.h | 3 + arch/s390/include/asm/pci_dma.h | 119 +--- arch/s390/pci/Makefile | 2 +- arch/s390/pci/pci.c | 22 +- arch/s390/pci/pci_bus.c | 5 - arch/s390/pci/pci_debug.c | 12 +- arch/s390/pci/pci_dma.c | 735 ------------------------ arch/s390/pci/pci_event.c | 17 +- arch/s390/pci/pci_sysfs.c | 19 +- drivers/iommu/Kconfig | 4 +- drivers/iommu/amd/iommu.c | 5 +- drivers/iommu/apple-dart.c | 5 +- drivers/iommu/dma-iommu.c | 191 ++++-- drivers/iommu/dma-iommu.h | 4 +- drivers/iommu/intel/iommu.c | 5 +- drivers/iommu/iommu.c | 38 +- drivers/iommu/msm_iommu.c | 5 +- drivers/iommu/mtk_iommu.c | 5 +- drivers/iommu/s390-iommu.c | 435 +++++++++++++- drivers/iommu/sprd-iommu.c | 5 +- drivers/iommu/sun50i-iommu.c | 4 +- drivers/iommu/tegra-gart.c | 5 +- drivers/s390/net/ism_drv.c | 2 +- include/linux/iommu.h | 29 +- 26 files changed, 682 insertions(+), 1010 deletions(-) --- base-commit: f1fcbaa18b28dec10281551dfe6ed3a3ed80e3d6 change-id: 20230310-dma_iommu-5e048c538647 Best regards, -- Niklas Schnelle Linux on Z Development IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Gregor Pillen Geschäftsführung: David Faller Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294 IBM Data Privacy Statement - https://www.ibm.com/privacy
