iommu/arm-smmu: Reintroduce locking around TLB sync operations

Commit 523d7423e21b ("iommu/arm-smmu: Remove io-pgtable spinlock")
removed the locking used to serialise map/unmap calls into the io-pgtable
code from the ARM SMMU driver. This is good for performance, but opens
us up to a nasty race with TLB syncs because the TLB sync register is
shared within a context bank (or even globally for stage-2 on SMMUv1).

There are two cases to consider:

  1. A CPU can be spinning on the completion of a TLB sync, take an
     interrupt which issues a subsequent TLB sync, and then report a
     timeout on return from the interrupt.

  2. A CPU can be spinning on the completion of a TLB sync, but other
     CPUs can continuously issue additional TLB syncs in such a way that
     the backoff logic reports a timeout.

Rather than fix this by spinning for completion of prior TLB syncs before
issuing a new one (which may suffer from fairness issues on large systems),
instead reintroduce locking around TLB sync operations in the ARM SMMU
driver.

Fixes: 523d7423e21b ("iommu/arm-smmu: Remove io-pgtable spinlock")
Cc: Robin Murphy <robin.murphy@arm.com>
Reported-by: Ray Jui <ray.jui@broadcom.com>
Tested-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index bc89b4d6c043..98ff462b5992 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -400,6 +400,8 @@ struct arm_smmu_device {
 
 	u32				cavium_id_base; /* Specific to Cavium */
 
+	spinlock_t			global_sync_lock;
+
 	/* IOMMU core code handle */
 	struct iommu_device		iommu;
 };
@@ -436,7 +438,7 @@ struct arm_smmu_domain {
 	struct arm_smmu_cfg		cfg;
 	enum arm_smmu_domain_stage	stage;
 	struct mutex			init_mutex; /* Protects smmu pointer */
-	spinlock_t			cb_lock; /* Serialises ATS1* ops */
+	spinlock_t			cb_lock; /* Serialises ATS1* ops and TLB syncs */
 	struct iommu_domain		domain;
 };
 
@@ -602,9 +604,12 @@ static void __arm_smmu_tlb_sync(struct arm_smmu_device *smmu,
 static void arm_smmu_tlb_sync_global(struct arm_smmu_device *smmu)
 {
 	void __iomem *base = ARM_SMMU_GR0(smmu);
+	unsigned long flags;
 
+	spin_lock_irqsave(&smmu->global_sync_lock, flags);
 	__arm_smmu_tlb_sync(smmu, base + ARM_SMMU_GR0_sTLBGSYNC,
 			    base + ARM_SMMU_GR0_sTLBGSTATUS);
+	spin_unlock_irqrestore(&smmu->global_sync_lock, flags);
 }
 
 static void arm_smmu_tlb_sync_context(void *cookie)
@@ -612,9 +617,12 @@ static void arm_smmu_tlb_sync_context(void *cookie)
 	struct arm_smmu_domain *smmu_domain = cookie;
 	struct arm_smmu_device *smmu = smmu_domain->smmu;
 	void __iomem *base = ARM_SMMU_CB(smmu, smmu_domain->cfg.cbndx);
+	unsigned long flags;
 
+	spin_lock_irqsave(&smmu_domain->cb_lock, flags);
 	__arm_smmu_tlb_sync(smmu, base + ARM_SMMU_CB_TLBSYNC,
 			    base + ARM_SMMU_CB_TLBSTATUS);
+	spin_unlock_irqrestore(&smmu_domain->cb_lock, flags);
 }
 
 static void arm_smmu_tlb_sync_vmid(void *cookie)
@@ -1925,6 +1933,7 @@ static int arm_smmu_device_cfg_probe(struct arm_smmu_device *smmu)
 
 	smmu->num_mapping_groups = size;
 	mutex_init(&smmu->stream_map_mutex);
+	spin_lock_init(&smmu->global_sync_lock);
 
 	if (smmu->version < ARM_SMMU_V2 || !(id & ID0_PTFS_NO_AARCH32)) {
 		smmu->features |= ARM_SMMU_FEAT_FMT_AARCH32_L;