iommu/arm-smmu: use mutex instead of spinlock for locking page tables

When creating IO mappings, we lazily allocate our page tables using the
standard, non-atomic allocator functions. This presents us with a
problem, since our page tables are protected with a spinlock.

This patch reworks the smmu_domain lock to use a mutex instead of a
spinlock. iova_to_phys is then reworked so that it only reads the page
tables, and can run in a lockless fashion, leaving the mutex to guard
against concurrent mapping threads.

Cc: <stable@vger.kernel.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 26 insertions, 36 deletions

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 1abfb5684ab7..6dbcaa4433cd 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -392,7 +392,7 @@ struct arm_smmu_domain {
         struct arm_smmu_cfg             root_cfg;
         phys_addr_t                     output_mask;
 
-        spinlock_t                      lock;
+        struct mutex                    lock;
 };
 
 static DEFINE_SPINLOCK(arm_smmu_devices_lock);
@@ -900,7 +900,7 @@ static int arm_smmu_domain_init(struct iommu_domain *domain)
                 goto out_free_domain;
         smmu_domain->root_cfg.pgd = pgd;
 
-        spin_lock_init(&smmu_domain->lock);
+        mutex_init(&smmu_domain->lock);
         domain->priv = smmu_domain;
         return 0;
 
@@ -1137,7 +1137,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
          * Sanity check the domain. We don't currently support domains
          * that cross between different SMMU chains.
          */
-        spin_lock(&smmu_domain->lock);
+        mutex_lock(&smmu_domain->lock);
         if (!smmu_domain->leaf_smmu) {
                 /* Now that we have a master, we can finalise the domain */
                 ret = arm_smmu_init_domain_context(domain, dev);
@@ -1152,7 +1152,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
                         dev_name(device_smmu->dev));
                 goto err_unlock;
         }
-        spin_unlock(&smmu_domain->lock);
+        mutex_unlock(&smmu_domain->lock);
 
         /* Looks ok, so add the device to the domain */
         master = find_smmu_master(smmu_domain->leaf_smmu, dev->of_node);
@@ -1162,7 +1162,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
         return arm_smmu_domain_add_master(smmu_domain, master);
 
 err_unlock:
-        spin_unlock(&smmu_domain->lock);
+        mutex_unlock(&smmu_domain->lock);
         return ret;
 }
 
@@ -1394,7 +1394,7 @@ static int arm_smmu_handle_mapping(struct arm_smmu_domain *smmu_domain,
         if (paddr & ~output_mask)
                 return -ERANGE;
 
-        spin_lock(&smmu_domain->lock);
+        mutex_lock(&smmu_domain->lock);
         pgd += pgd_index(iova);
         end = iova + size;
         do {
@@ -1410,7 +1410,7 @@ static int arm_smmu_handle_mapping(struct arm_smmu_domain *smmu_domain,
         } while (pgd++, iova != end);
 
 out_unlock:
-        spin_unlock(&smmu_domain->lock);
+        mutex_unlock(&smmu_domain->lock);
 
         /* Ensure new page tables are visible to the hardware walker */
         if (smmu->features & ARM_SMMU_FEAT_COHERENT_WALK)
@@ -1449,44 +1449,34 @@ static size_t arm_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
 static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
                                          dma_addr_t iova)
 {
-        pgd_t *pgd;
-        pud_t *pud;
-        pmd_t *pmd;
-        pte_t *pte;
+        pgd_t *pgdp, pgd;
+        pud_t pud;
+        pmd_t pmd;
+        pte_t pte;
         struct arm_smmu_domain *smmu_domain = domain->priv;
         struct arm_smmu_cfg *root_cfg = &smmu_domain->root_cfg;
-        struct arm_smmu_device *smmu = root_cfg->smmu;
 
-        spin_lock(&smmu_domain->lock);
-        pgd = root_cfg->pgd;
-        if (!pgd)
-                goto err_unlock;
+        pgdp = root_cfg->pgd;
+        if (!pgdp)
+                return 0;
 
-        pgd += pgd_index(iova);
-        if (pgd_none_or_clear_bad(pgd))
-                goto err_unlock;
+        pgd = *(pgdp + pgd_index(iova));
+        if (pgd_none(pgd))
+                return 0;
 
-        pud = pud_offset(pgd, iova);
-        if (pud_none_or_clear_bad(pud))
-                goto err_unlock;
+        pud = *pud_offset(&pgd, iova);
+        if (pud_none(pud))
+                return 0;
 
-        pmd = pmd_offset(pud, iova);
-        if (pmd_none_or_clear_bad(pmd))
-                goto err_unlock;
+        pmd = *pmd_offset(&pud, iova);
+        if (pmd_none(pmd))
+                return 0;
 
-        pte = pmd_page_vaddr(*pmd) + pte_index(iova);
+        pte = *(pmd_page_vaddr(pmd) + pte_index(iova));
         if (pte_none(pte))
-                goto err_unlock;
-
-        spin_unlock(&smmu_domain->lock);
-        return __pfn_to_phys(pte_pfn(*pte)) | (iova & ~PAGE_MASK);
+                return 0;
 
-err_unlock:
-        spin_unlock(&smmu_domain->lock);
-        dev_warn(smmu->dev,
-                 "invalid (corrupt?) page tables detected for iova 0x%llx\n",
-                 (unsigned long long)iova);
-        return -EINVAL;
+        return __pfn_to_phys(pte_pfn(pte)) | (iova & ~PAGE_MASK);
 }
 
 static int arm_smmu_domain_has_cap(struct iommu_domain *domain,