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Subject[PATCH 4/4] iommu/tegra-smmu: Prevent race condition between map and unmap
Date
When testing with ethernet downloading, "EMEM address decode error"
happens due to race condition between map() and unmap() functions.

This patch adds a spin lock to protect content within as->[count]
and as->pts[pde] references, since a function call might be atomic.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
---
drivers/iommu/tegra-smmu.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index 3999ecb63cfa..236bc6d6d238 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -37,6 +37,7 @@ struct tegra_smmu {

unsigned long *asids;
struct mutex lock;
+ spinlock_t as_lock;

struct list_head list;

@@ -664,17 +665,23 @@ static int tegra_smmu_map(struct iommu_domain *domain, unsigned long iova,
phys_addr_t paddr, size_t size, int prot, gfp_t gfp)
{
struct tegra_smmu_as *as = to_smmu_as(domain);
+ struct tegra_smmu *smmu = as->smmu;
+ unsigned long flags;
dma_addr_t pte_dma;
u32 pte_attrs;
u32 *pte;

+ spin_lock_irqsave(&smmu->as_lock, flags);
pte = as_get_pte(as, iova, &pte_dma);
- if (!pte)
+ if (!pte) {
+ spin_unlock_irqrestore(&smmu->as_lock, flags);
return -ENOMEM;
+ }

/* If we aren't overwriting a pre-existing entry, increment use */
if (*pte == 0)
tegra_smmu_pte_get_use(as, iova);
+ spin_unlock_irqrestore(&smmu->as_lock, flags);

pte_attrs = SMMU_PTE_NONSECURE;

@@ -694,6 +701,8 @@ static size_t tegra_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
size_t size, struct iommu_iotlb_gather *gather)
{
struct tegra_smmu_as *as = to_smmu_as(domain);
+ struct tegra_smmu *smmu = as->smmu;
+ unsigned long flags;
dma_addr_t pte_dma;
u32 *pte;

@@ -702,7 +711,10 @@ static size_t tegra_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
return 0;

tegra_smmu_set_pte(as, iova, pte, pte_dma, 0);
+
+ spin_lock_irqsave(&smmu->as_lock, flags);
tegra_smmu_pte_put_use(as, iova);
+ spin_unlock_irqrestore(&smmu->as_lock, flags);

return size;
}
@@ -1033,6 +1045,7 @@ struct tegra_smmu *tegra_smmu_probe(struct device *dev,

INIT_LIST_HEAD(&smmu->groups);
mutex_init(&smmu->lock);
+ spin_lock_init(&smmu->as_lock);

smmu->regs = mc->regs;
smmu->soc = soc;
--
2.17.1
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