[PATCH v4] iommu/tegra-smmu: Add locking around mapping operations

[Dmitry Osipenko]

The mapping operations of the Tegra SMMU driver are subjected to a race
condition issues because SMMU Address Space isn't allocated and freed
atomically, while it should be. This patch makes the mapping operations
atomic, it fixes an accidentally released Host1x Address Space problem
which happens while running multiple graphics tests in parallel on
Tegra30, i.e. by having multiple threads racing with each other in the
Host1x's submission and completion code paths, performing IOVA mappings
and unmappings in parallel.

Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
---

Changelog:

v4: - Returned to use spinlock, but now using a smarter allocation
      logic that performs allocation in a sleeping context whenever
      possible.

    - Removed the stable tag because patch isn't portable as-is
      since the arguments of map/unmap() callbacks changed recently.
      Perhaps we could just ignore older kernels for now. It will be
      possible to fix older kernels with a custom patch if will be needed.

v3: - No changes. Resending for visibility.

v2: - Now using mutex instead of spinlock.

    - The _locked postfix is replaced with the underscores prefix.

 drivers/iommu/tegra-smmu.c | 95 +++++++++++++++++++++++++++++++++-----
 1 file changed, 84 insertions(+), 11 deletions(-)

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index 124c8848ab7e..b5914356b878 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -12,6 +12,7 @@
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/dma-mapping.h>
 
 #include <soc/tegra/ahb.h>
@@ -49,6 +50,7 @@ struct tegra_smmu_as {
 	struct iommu_domain domain;
 	struct tegra_smmu *smmu;
 	unsigned int use_count;
+	spinlock_t lock;
 	u32 *count;
 	struct page **pts;
 	struct page *pd;
@@ -308,6 +310,8 @@ static struct iommu_domain *tegra_smmu_domain_alloc(unsigned type)
 		return NULL;
 	}
 
+	spin_lock_init(&as->lock);
+
 	/* setup aperture */
 	as->domain.geometry.aperture_start = 0;
 	as->domain.geometry.aperture_end = 0xffffffff;
@@ -569,19 +573,14 @@ static u32 *tegra_smmu_pte_lookup(struct tegra_smmu_as *as, unsigned long iova,
 }
 
 static u32 *as_get_pte(struct tegra_smmu_as *as, dma_addr_t iova,
-		       dma_addr_t *dmap)
+		       dma_addr_t *dmap, struct page *page)
 {
 	unsigned int pde = iova_pd_index(iova);
 	struct tegra_smmu *smmu = as->smmu;
 
 	if (!as->pts[pde]) {
-		struct page *page;
 		dma_addr_t dma;
 
-		page = alloc_page(GFP_KERNEL | __GFP_DMA | __GFP_ZERO);
-		if (!page)
-			return NULL;
-
 		dma = dma_map_page(smmu->dev, page, 0, SMMU_SIZE_PT,
 				   DMA_TO_DEVICE);
 		if (dma_mapping_error(smmu->dev, dma)) {
@@ -655,15 +654,61 @@ static void tegra_smmu_set_pte(struct tegra_smmu_as *as, unsigned long iova,
 	smmu_flush(smmu);
 }
 
-static int tegra_smmu_map(struct iommu_domain *domain, unsigned long iova,
-			  phys_addr_t paddr, size_t size, int prot, gfp_t gfp)
+static struct page *as_get_pde_page(struct tegra_smmu_as *as,
+				    unsigned long iova, gfp_t gfp,
+				    unsigned long *flags)
+{
+	unsigned int pde = iova_pd_index(iova);
+	struct page *page = as->pts[pde];
+
+	/* at first check whether allocation needs to be done at all */
+	if (page)
+		return page;
+
+	/*
+	 * In order to prevent exhaustion of the atomic memory pool, we
+	 * allocate page in a sleeping context if GFP flags permit. Hence
+	 * spinlock needs to be unlocked and re-locked after allocation.
+	 */
+	if (!(gfp & GFP_NOWAIT))
+		spin_unlock_irqrestore(&as->lock, *flags);
+
+	page = alloc_page(gfp | __GFP_DMA | __GFP_ZERO);
+
+	if (!(gfp & GFP_NOWAIT))
+		spin_lock_irqsave(&as->lock, *flags);
+
+	/*
+	 * In a case of blocking allocation, a concurrent mapping may win
+	 * the PDE allocation. In this case the allocated page isn't needed
+	 * if allocation succeeded and the allocation failure isn't fatal.
+	 */
+	if (as->pts[pde]) {
+		if (page)
+			__free_page(page);
+
+		page = as->pts[pde];
+	}
+
+	return page;
+}
+
+static int
+__tegra_smmu_map(struct iommu_domain *domain, unsigned long iova,
+		 phys_addr_t paddr, size_t size, int prot, gfp_t gfp,
+		 unsigned long *flags)
 {
 	struct tegra_smmu_as *as = to_smmu_as(domain);
 	dma_addr_t pte_dma;
+	struct page *page;
 	u32 pte_attrs;
 	u32 *pte;
 
-	pte = as_get_pte(as, iova, &pte_dma);
+	page = as_get_pde_page(as, iova, gfp, flags);
+	if (!page)
+		return -ENOMEM;
+
+	pte = as_get_pte(as, iova, &pte_dma, page);
 	if (!pte)
 		return -ENOMEM;
 
@@ -685,8 +730,9 @@ static int tegra_smmu_map(struct iommu_domain *domain, unsigned long iova,
 	return 0;
 }
 
-static size_t tegra_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
-			       size_t size, struct iommu_iotlb_gather *gather)
+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);
 	dma_addr_t pte_dma;
@@ -702,6 +748,33 @@ static size_t tegra_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
 	return size;
 }
 
+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);
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&as->lock, flags);
+	ret = __tegra_smmu_map(domain, iova, paddr, size, prot, gfp, &flags);
+	spin_unlock_irqrestore(&as->lock, flags);
+
+	return ret;
+}
+
+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);
+	unsigned long flags;
+
+	spin_lock_irqsave(&as->lock, flags);
+	size = __tegra_smmu_unmap(domain, iova, size, gather);
+	spin_unlock_irqrestore(&as->lock, flags);
+
+	return size;
+}
+
 static phys_addr_t tegra_smmu_iova_to_phys(struct iommu_domain *domain,
 					   dma_addr_t iova)
 {
-- 
2.27.0