[PATCH 5.11 402/601] dma-iommu: use static-key to minimize the impact in the fast-path

Greg Kroah-Hartman
2021-05-12T17:41:48Z

From: Lianbo Jiang <lijiang@redhat.com>

[ Upstream commit a8e8af35c9f4f75f981a95488c7066d31bac4bef ]

Let's move out the is_kdump_kernel() check from iommu_dma_deferred_attach()
to iommu_dma_init(), and use the static-key in the fast-path to minimize
the impact in the normal case.

Co-developed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20210126115337.20068-2-lijiang@redhat.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/iommu/dma-iommu.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 00fbc591a142..07e7b2f3ba27 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -51,6 +51,8 @@ struct iommu_dma_cookie {
struct iommu_domain *fq_domain;
};

+static DEFINE_STATIC_KEY_FALSE(iommu_deferred_attach_enabled);
+
void iommu_dma_free_cpu_cached_iovas(unsigned int cpu,
struct iommu_domain *domain)
{
@@ -389,9 +391,6 @@ static int iommu_dma_deferred_attach(struct device *dev,
{
const struct iommu_ops *ops = domain->ops;

- if (!is_kdump_kernel())
- return 0;
-
if (unlikely(ops->is_attach_deferred &&
ops->is_attach_deferred(domain, dev)))
return iommu_attach_device(domain, dev);
@@ -536,7 +535,8 @@ static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
size_t iova_off = iova_offset(iovad, phys);
dma_addr_t iova;

- if (unlikely(iommu_dma_deferred_attach(dev, domain)))
+ if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
+ iommu_dma_deferred_attach(dev, domain))
return DMA_MAPPING_ERROR;

size = iova_align(iovad, size + iova_off);
@@ -694,7 +694,8 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,

*dma_handle = DMA_MAPPING_ERROR;

- if (unlikely(iommu_dma_deferred_attach(dev, domain)))
+ if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
+ iommu_dma_deferred_attach(dev, domain))
return NULL;

min_size = alloc_sizes & -alloc_sizes;
@@ -977,7 +978,8 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
unsigned long mask = dma_get_seg_boundary(dev);
int i;

- if (unlikely(iommu_dma_deferred_attach(dev, domain)))
+ if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
+ iommu_dma_deferred_attach(dev, domain))
return 0;

if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
@@ -1425,6 +1427,9 @@ void iommu_dma_compose_msi_msg(struct msi_desc *desc,

static int iommu_dma_init(void)
{
+ if (is_kdump_kernel())
+ static_branch_enable(&iommu_deferred_attach_enabled);
+
return iova_cache_get();
}
arch_initcall(iommu_dma_init);
--
2.30.2