From 73559ad33270a0fa8169c262a467cb17e53e03f1 Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Wed, 12 Sep 2018 16:24:12 +0100 Subject: [PATCH 1587/2944] iommu: Add fast hook for getting DMA domains fix #27432135 commit 6af588fed39178c8e118fcf9cb6664e58a1fbe88 upstream While iommu_get_domain_for_dev() is the robust way for arbitrary IOMMU API callers to retrieve the domain pointer, for DMA ops domains it doesn't scale well for large systems and multi-queue devices, since the momentary refcount adjustment will lead to exclusive cacheline contention when multiple CPUs are operating in parallel on different mappings for the same device. In the case of DMA ops domains, however, this refcounting is actually unnecessary, since they already imply that the group exists and is managed by platform code and IOMMU internals (by virtue of iommu_group_get_for_dev()) such that a reference will already be held for the lifetime of the device. Thus we can avoid the bottleneck by providing a fast lookup specifically for the DMA code to retrieve the default domain it already knows it has set up - a simple read-only dereference plays much nicer with cache-coherency protocols. Signed-off-by: Robin Murphy Tested-by: Will Deacon Signed-off-by: Joerg Roedel Signed-off-by: Rongwei Wang Acked-by: zou cao --- drivers/iommu/iommu.c | 9 +++++++++ include/linux/iommu.h | 1 + 2 files changed, 10 insertions(+) diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index b2b973b..5c11e70 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -1432,6 +1432,15 @@ struct iommu_domain *iommu_get_domain_for_dev(struct device *dev) EXPORT_SYMBOL_GPL(iommu_get_domain_for_dev); /* + * For IOMMU_DOMAIN_DMA implementations which already provide their own + * guarantees that the group and its default domain are valid and correct. + */ +struct iommu_domain *iommu_get_dma_domain(struct device *dev) +{ + return dev->iommu_group->default_domain; +} + +/* * IOMMU groups are really the natrual working unit of the IOMMU, but * the IOMMU API works on domains and devices. Bridge that gap by * iterating over the devices in a group. Ideally we'd have a single diff --git a/include/linux/iommu.h b/include/linux/iommu.h index decabe8..e0a027f 100644 --- a/include/linux/iommu.h +++ b/include/linux/iommu.h @@ -294,6 +294,7 @@ extern int iommu_attach_device(struct iommu_domain *domain, extern void iommu_detach_device(struct iommu_domain *domain, struct device *dev); extern struct iommu_domain *iommu_get_domain_for_dev(struct device *dev); +extern struct iommu_domain *iommu_get_dma_domain(struct device *dev); extern int iommu_map(struct iommu_domain *domain, unsigned long iova, phys_addr_t paddr, size_t size, int prot); extern size_t iommu_unmap(struct iommu_domain *domain, unsigned long iova, -- 1.8.3.1