iommu/tegra: smmu: Fix unsleepable memory allocation at alloc_pdir()

alloc_pdir() is called from smmu_iommu_domain_init() with spin_lock
held. memory allocations in alloc_pdir() had to be atomic. Instead of
converting into atomic allocation, this patch once releases a lock,
does the allocation, holds the lock again and then sees if it's raced
or not in order to avoid introducing mutex and preallocation.

Signed-off-by: Hiroshi DOYU <hdoyu@nvidia.com>
Reported-by: Chris Wright <chrisw@sous-sol.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

1 files changed, 45 insertions, 32 deletions

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index 68441fcca261..68a15a0d5b8a 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -555,28 +555,39 @@ static inline void put_signature(struct smmu_as *as,
 /*
  * Caller must lock/unlock as
  */
-static int alloc_pdir(struct smmu_as *as)
+static int alloc_pdir(struct smmu_as *as, unsigned long *flags)
 {
         unsigned long *pdir;
-        int pdn;
+        int pdn, err = 0;
         u32 val;
         struct smmu_device *smmu = as->smmu;
+        struct page *page;
+        unsigned int *cnt;
 
-        as->pte_count = devm_kzalloc(smmu->dev,
-                     sizeof(as->pte_count[0]) * SMMU_PDIR_COUNT, GFP_KERNEL);
-        if (!as->pte_count) {
-                dev_err(smmu->dev,
-                        "failed to allocate smmu_device PTE cunters\n");
-                return -ENOMEM;
+        /*
+         * do the allocation outside the as->lock
+         */
+        spin_unlock_irqrestore(&as->lock, *flags);
+        cnt = devm_kzalloc(smmu->dev,
+                           sizeof(cnt[0]) * SMMU_PDIR_COUNT, GFP_KERNEL);
+        page = alloc_page(GFP_KERNEL | __GFP_DMA);
+        spin_lock_irqsave(&as->lock, *flags);
+
+        if (as->pdir_page) {
+                /* We raced, free the redundant */
+                err = -EAGAIN;
+                goto err_out;
         }
-        as->pdir_page = alloc_page(GFP_KERNEL | __GFP_DMA);
-        if (!as->pdir_page) {
-                dev_err(smmu->dev,
-                        "failed to allocate smmu_device page directory\n");
-                devm_kfree(smmu->dev, as->pte_count);
-                as->pte_count = NULL;
-                return -ENOMEM;
+
+        if (!page || !cnt) {
+                dev_err(smmu->dev, "failed to allocate at %s\n", __func__);
+                err = -ENOMEM;
+                goto err_out;
         }
+
+        as->pdir_page = page;
+        as->pte_count = cnt;
+
         SetPageReserved(as->pdir_page);
         pdir = page_address(as->pdir_page);
 
@@ -593,6 +604,12 @@ static int alloc_pdir(struct smmu_as *as)
         FLUSH_SMMU_REGS(as->smmu);
 
         return 0;
+
+err_out:
+        devm_kfree(smmu->dev, cnt);
+        if (page)
+                __free_page(page);
+        return err;
 }
 
 static void __smmu_iommu_unmap(struct smmu_as *as, dma_addr_t iova)
@@ -784,29 +801,29 @@ out:
 
 static int smmu_iommu_domain_init(struct iommu_domain *domain)
 {
-        int i;
+        int i, err = -ENODEV;
         unsigned long flags;
         struct smmu_as *as;
         struct smmu_device *smmu = smmu_handle;
 
         /* Look for a free AS with lock held */
         for  (i = 0; i < smmu->num_as; i++) {
-                struct smmu_as *tmp = &smmu->as[i];
-
-                spin_lock_irqsave(&tmp->lock, flags);
-                if (!tmp->pdir_page) {
-                        as = tmp;
-                        goto found;
+                as = &smmu->as[i];
+                spin_lock_irqsave(&as->lock, flags);
+                if (!as->pdir_page) {
+                        err = alloc_pdir(as, &flags);
+                        if (!err)
+                                goto found;
                 }
-                spin_unlock_irqrestore(&tmp->lock, flags);
+                spin_unlock_irqrestore(&as->lock, flags);
+                if (err != -EAGAIN)
+                        break;
         }
-        dev_err(smmu->dev, "no free AS\n");
-        return -ENODEV;
+        if (i == smmu->num_as)
+                dev_err(smmu->dev,  "no free AS\n");
+        return err;
 
 found:
-        if (alloc_pdir(as) < 0)
-                goto err_alloc_pdir;
-
         spin_lock(&smmu->lock);
 
         /* Update PDIR register */
@@ -822,10 +839,6 @@ found:
 
         dev_dbg(smmu->dev, "smmu_as@%p\n", as);
         return 0;
-
-err_alloc_pdir:
-        spin_unlock_irqrestore(&as->lock, flags);
-        return -ENODEV;
 }
 
 static void smmu_iommu_domain_destroy(struct iommu_domain *domain)