[PATCH V2 2/6] iommu: iova: properly handle 0 as a valid IOVA address

[Ajay Kumar]

From: Marek Szyprowski <m.szyprowski at samsung.com>

Zero is a valid DMA and IOVA address on many architectures, so adjust the
IOVA management code to properly handle it. A new value IOVA_BAD_ADDR
(~0UL) is introduced as a generic value for the error case. Adjust all
callers of the alloc_iova_fast() function for the new return value.

Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
Signed-off-by: Ajay Kumar <ajaykumar.rs at samsung.com>
---
 drivers/iommu/dma-iommu.c | 16 +++++++++-------
 drivers/iommu/iova.c      | 13 +++++++++----
 include/linux/iova.h      |  1 +
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 1ca85d37eeab..16218d6a0703 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -605,7 +605,7 @@ static dma_addr_t iommu_dma_alloc_iova(struct iommu_domain *domain,
 {
 	struct iommu_dma_cookie *cookie = domain->iova_cookie;
 	struct iova_domain *iovad = &cookie->iovad;
-	unsigned long shift, iova_len, iova = 0;
+	unsigned long shift, iova_len, iova = IOVA_BAD_ADDR;
 
 	if (cookie->type == IOMMU_DMA_MSI_COOKIE) {
 		cookie->msi_iova += size;
@@ -625,11 +625,13 @@ static dma_addr_t iommu_dma_alloc_iova(struct iommu_domain *domain,
 		iova = alloc_iova_fast(iovad, iova_len,
 				       DMA_BIT_MASK(32) >> shift, false);
 
-	if (!iova)
+	if (iova == IOVA_BAD_ADDR)
 		iova = alloc_iova_fast(iovad, iova_len, dma_limit >> shift,
 				       true);
 
-	return (dma_addr_t)iova << shift;
+	if (iova != IOVA_BAD_ADDR)
+		return (dma_addr_t)iova << shift;
+	return DMA_MAPPING_ERROR;
 }
 
 static void iommu_dma_free_iova(struct iommu_dma_cookie *cookie,
@@ -688,7 +690,7 @@ static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
 	size = iova_align(iovad, size + iova_off);
 
 	iova = iommu_dma_alloc_iova(domain, size, dma_mask, dev);
-	if (!iova)
+	if (iova == DMA_MAPPING_ERROR)
 		return DMA_MAPPING_ERROR;
 
 	if (iommu_map_atomic(domain, iova, phys - iova_off, size, prot)) {
@@ -799,7 +801,7 @@ static struct page **__iommu_dma_alloc_noncontiguous(struct device *dev,
 
 	size = iova_align(iovad, size);
 	iova = iommu_dma_alloc_iova(domain, size, dev->coherent_dma_mask, dev);
-	if (!iova)
+	if (iova == DMA_MAPPING_ERROR)
 		goto out_free_pages;
 
 	if (sg_alloc_table_from_pages(sgt, pages, count, 0, size, GFP_KERNEL))
@@ -1204,7 +1206,7 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
 	}
 
 	iova = iommu_dma_alloc_iova(domain, iova_len, dma_get_mask(dev), dev);
-	if (!iova) {
+	if (iova == DMA_MAPPING_ERROR) {
 		ret = -ENOMEM;
 		goto out_restore_sg;
 	}
@@ -1516,7 +1518,7 @@ static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
 		return NULL;
 
 	iova = iommu_dma_alloc_iova(domain, size, dma_get_mask(dev), dev);
-	if (!iova)
+	if (iova == DMA_MAPPING_ERROR)
 		goto out_free_page;
 
 	if (iommu_map(domain, iova, msi_addr, size, prot))
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index db77aa675145..ae0fe0a6714e 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -429,6 +429,8 @@ EXPORT_SYMBOL_GPL(free_iova);
  * This function tries to satisfy an iova allocation from the rcache,
  * and falls back to regular allocation on failure. If regular allocation
  * fails too and the flush_rcache flag is set then the rcache will be flushed.
+ * Returns a pfn the allocated iova starts at or IOVA_BAD_ADDR in the case
+ * of a failure.
 */
 unsigned long
 alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
@@ -447,7 +449,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
 		size = roundup_pow_of_two(size);
 
 	iova_pfn = iova_rcache_get(iovad, size, limit_pfn + 1);
-	if (iova_pfn)
+	if (iova_pfn != IOVA_BAD_ADDR)
 		return iova_pfn;
 
 retry:
@@ -456,7 +458,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
 		unsigned int cpu;
 
 		if (!flush_rcache)
-			return 0;
+			return IOVA_BAD_ADDR;
 
 		/* Try replenishing IOVAs by flushing rcache. */
 		flush_rcache = false;
@@ -831,7 +833,7 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache,
 				       unsigned long limit_pfn)
 {
 	struct iova_cpu_rcache *cpu_rcache;
-	unsigned long iova_pfn = 0;
+	unsigned long iova_pfn = IOVA_BAD_ADDR;
 	bool has_pfn = false;
 	unsigned long flags;
 
@@ -858,6 +860,9 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache,
 
 	spin_unlock_irqrestore(&cpu_rcache->lock, flags);
 
+	if (!iova_pfn)
+		return IOVA_BAD_ADDR;
+
 	return iova_pfn;
 }
 
@@ -873,7 +878,7 @@ static unsigned long iova_rcache_get(struct iova_domain *iovad,
 	unsigned int log_size = order_base_2(size);
 
 	if (log_size >= IOVA_RANGE_CACHE_MAX_SIZE || !iovad->rcaches)
-		return 0;
+		return IOVA_BAD_ADDR;
 
 	return __iova_rcache_get(&iovad->rcaches[log_size], limit_pfn - size);
 }
diff --git a/include/linux/iova.h b/include/linux/iova.h
index 320a70e40233..46b5b10c532b 100644
--- a/include/linux/iova.h
+++ b/include/linux/iova.h
@@ -21,6 +21,7 @@ struct iova {
 	unsigned long	pfn_lo; /* Lowest allocated pfn */
 };
 
+#define IOVA_BAD_ADDR	(~0UL)
 
 struct iova_rcache;
 
-- 
2.17.1