[PATCH v6 19/19] swiotlb-xen: instead of bouncing on the swiotlb, pin single pages

[Stefano Stabellini]

If we are dealing with single page mappings that don't cross page
boundaries, we can try to pin the page and get the corresponding mfn,
using xen_pin_page.  This avoids going through the swiotlb bounce
buffer.  If xen_pin_page fails (because the underlying mfn doesn't
respect the dma_mask) fall back to the swiotlb bounce buffer.
Add a ref count to xen_dma_info, so that we can avoid pinnig pages that
are already pinned.
Use a spinlock to protect accesses, insertions and deletions in the
rbtrees.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 drivers/xen/swiotlb-xen.c |  152 ++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 143 insertions(+), 9 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 022bcaf..6f94285 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -57,6 +57,8 @@
 #define NR_DMA_SEGS  ((xen_io_tlb_nslabs + IO_TLB_SEGSIZE - 1) / IO_TLB_SEGSIZE)
 static char *xen_io_tlb_start, *xen_io_tlb_end;
 static unsigned long xen_io_tlb_nslabs;
+spinlock_t swiotlb_lock;
+
 /*
  * Quick lookup value of the bus address of the IOTLB.
  */
@@ -79,6 +81,7 @@ struct xen_dma_info {
 	dma_addr_t dma_addr;
 	phys_addr_t phys_addr;
 	size_t size;
+	atomic_t refs;
 	struct rb_node rbnode_dma;
 	struct rb_node rbnode_phys;
 };
@@ -254,6 +257,48 @@ static dma_addr_t xen_virt_to_bus(void *address)
 	return xen_phys_to_bus_quick(virt_to_phys(address));
 }
 
+static int xen_pin_dev_page(struct device *dev,
+							phys_addr_t phys,
+							dma_addr_t *dev_addr)
+{
+	u64 dma_mask = DMA_BIT_MASK(32);
+	xen_pfn_t in;
+	struct xen_dma_info *dma_info = xen_get_dma_info_from_phys(phys);
+
+	if (dma_info != NULL) {
+		atomic_inc(&dma_info->refs);
+		*dev_addr = dma_info->dma_addr + (phys - dma_info->phys_addr);
+		return 0;
+	}
+
+	if (dev && dev->coherent_dma_mask)
+		dma_mask = dma_alloc_coherent_mask(dev, GFP_KERNEL);
+
+	in = phys >> PAGE_SHIFT;
+	if (!xen_pin_page(&in, fls64(dma_mask))) {
+		*dev_addr = in << PAGE_SHIFT;
+		dma_info = kzalloc(sizeof(struct xen_dma_info), GFP_NOWAIT);
+		if (!dma_info) {
+			pr_warn("cannot allocate xen_dma_info\n");
+			xen_destroy_contiguous_region(phys & PAGE_MASK, 0);
+			return -ENOMEM;
+		}
+		dma_info->phys_addr = phys & PAGE_MASK;
+		dma_info->size = PAGE_SIZE;
+		dma_info->dma_addr = *dev_addr;
+		if (xen_dma_add_entry(dma_info)) {
+			pr_warn("cannot add new entry to bus_to_phys\n");
+			xen_destroy_contiguous_region(phys & PAGE_MASK, 0);
+			kfree(dma_info);
+			return -EFAULT;
+		}
+		atomic_set(&dma_info->refs, 1);
+		*dev_addr += (phys & ~PAGE_MASK);
+		return 0;
+	}
+	return -EFAULT;
+}
+
 static int check_pages_physically_contiguous(unsigned long pfn,
 					     unsigned int offset,
 					     size_t length)
@@ -434,6 +479,7 @@ retry:
 		rc = 0;
 	} else
 		rc = swiotlb_late_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs);
+	spin_lock_init(&swiotlb_lock);
 	return rc;
 error:
 	if (repeat--) {
@@ -461,6 +507,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 	phys_addr_t phys;
 	dma_addr_t dev_addr;
 	struct xen_dma_info *dma_info = NULL;
+	unsigned long irqflags;
 
 	/*
 	* Ignore region specifiers - the kernel's ideas of
@@ -497,7 +544,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 	    !range_straddles_page_boundary(phys, size))
 		*dma_handle = dev_addr;
 	else {
-		if (xen_create_contiguous_region(phys, order,
+		if (xen_create_contiguous_region(phys & PAGE_MASK, order,
 						 fls64(dma_mask), dma_handle) != 0) {
 			xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
 			return NULL;
@@ -509,15 +556,19 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 			xen_destroy_contiguous_region(phys, order);
 			return NULL;
 		}
-		dma_info->phys_addr = phys;
-		dma_info->size = size;
+		dma_info->phys_addr = phys & PAGE_MASK;
+		dma_info->size = (1U << order) << PAGE_SHIFT;
 		dma_info->dma_addr = *dma_handle;
+		atomic_set(&dma_info->refs, 1);
+		spin_lock_irqsave(&swiotlb_lock, irqflags);
 		if (xen_dma_add_entry(dma_info)) {
+			spin_unlock_irqrestore(&swiotlb_lock, irqflags);
 			pr_warn("cannot add new entry to bus_to_phys\n");
 			xen_destroy_contiguous_region(phys, order);
 			kfree(dma_info);
 			return NULL;
 		}
+		spin_unlock_irqrestore(&swiotlb_lock, irqflags);
 	}
 	memset(ret, 0, size);
 	return ret;
@@ -532,6 +583,7 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 	phys_addr_t phys;
 	u64 dma_mask = DMA_BIT_MASK(32);
 	struct xen_dma_info *dma_info = NULL;
+	unsigned long flags;
 
 	if (dma_release_from_coherent(hwdev, order, vaddr))
 		return;
@@ -539,6 +591,7 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 	if (hwdev && hwdev->coherent_dma_mask)
 		dma_mask = hwdev->coherent_dma_mask;
 
+	spin_lock_irqsave(&swiotlb_lock, flags);
 	/* do not use virt_to_phys because on ARM it doesn't return you the
 	 * physical address */
 	phys = xen_bus_to_phys(dev_addr);
@@ -546,12 +599,16 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 	if (xen_feature(XENFEAT_auto_translated_physmap) ||
 		(((dev_addr + size - 1 > dma_mask)) ||
 		 range_straddles_page_boundary(phys, size))) {
-		xen_destroy_contiguous_region(phys, order);
 		dma_info = xen_get_dma_info_from_dma(dev_addr);
-		rb_erase(&dma_info->rbnode, &bus_to_phys);
-		kfree(dma_info);
+		if (atomic_dec_and_test(&dma_info->refs)) {
+			xen_destroy_contiguous_region(phys & PAGE_MASK, order);
+			rb_erase(&dma_info->rbnode_dma, &bus_to_phys);
+			rb_erase(&dma_info->rbnode_phys, &phys_to_bus);
+			kfree(dma_info);
+		}
 	}
 
+	spin_unlock_irqrestore(&swiotlb_lock, flags);
 	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_free_coherent);
@@ -583,6 +640,23 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 	    !range_straddles_page_boundary(phys, size) && !swiotlb_force)
 		return dev_addr;
 
+	if (xen_feature(XENFEAT_auto_translated_physmap) &&
+		size <= PAGE_SIZE &&
+		!range_straddles_page_boundary(phys, size) &&
+		!swiotlb_force) {
+		unsigned long flags;
+		int rc;
+
+		spin_lock_irqsave(&swiotlb_lock, flags);
+		rc = xen_pin_dev_page(dev, phys, &dev_addr);
+		spin_unlock_irqrestore(&swiotlb_lock, flags);
+
+		if (!rc) {
+			dma_mark_clean(phys_to_virt(phys), size);
+			return dev_addr;
+		}
+	}
+
 	/*
 	 * Oh well, have to allocate and map a bounce buffer.
 	 * Pass the dma_addr of the first slab in the iotlb buffer as
@@ -618,10 +692,37 @@ EXPORT_SYMBOL_GPL(xen_swiotlb_map_page);
 static void xen_unmap_single(struct device *hwdev, dma_addr_t dev_addr,
 			     size_t size, enum dma_data_direction dir)
 {
-	phys_addr_t paddr = xen_bus_to_phys(dev_addr);
+	struct xen_dma_info *dma_info;
+	phys_addr_t paddr = DMA_ERROR_CODE;
+	char *vaddr = NULL;
+	unsigned long flags;
 
 	BUG_ON(dir == DMA_NONE);
 
+	spin_lock_irqsave(&swiotlb_lock, flags);
+	dma_info = xen_get_dma_info_from_dma(dev_addr);
+	if (dma_info != NULL) {
+		paddr = dma_info->phys_addr + (dev_addr - dma_info->dma_addr);
+		vaddr = phys_to_virt(paddr);
+	}
+
+	if (xen_feature(XENFEAT_auto_translated_physmap) &&
+		paddr != DMA_ERROR_CODE &&
+		!(vaddr >= xen_io_tlb_start && vaddr < xen_io_tlb_end) &&
+		!swiotlb_force) {
+		if (atomic_dec_and_test(&dma_info->refs)) {
+			xen_destroy_contiguous_region(paddr & PAGE_MASK, 0);
+			rb_erase(&dma_info->rbnode_dma, &bus_to_phys);
+			rb_erase(&dma_info->rbnode_phys, &phys_to_bus);
+			kfree(dma_info);
+		}
+		spin_unlock_irqrestore(&swiotlb_lock, flags);
+		if ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL))
+			dma_mark_clean(vaddr, size);
+		return;
+	}
+	spin_unlock_irqrestore(&swiotlb_lock, flags);
+
 	/* NOTE: We use dev_addr here, not paddr! */
 	if (is_xen_swiotlb_buffer(dev_addr)) {
 		swiotlb_tbl_unmap_single(hwdev, paddr, size, dir);
@@ -664,9 +765,19 @@ xen_swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
 			enum dma_sync_target target)
 {
 	phys_addr_t paddr = xen_bus_to_phys(dev_addr);
+	char *vaddr = phys_to_virt(paddr);
 
 	BUG_ON(dir == DMA_NONE);
 
+	if (xen_feature(XENFEAT_auto_translated_physmap) &&
+		paddr != DMA_ERROR_CODE &&
+		size <= PAGE_SIZE &&
+		!(vaddr >= xen_io_tlb_start && vaddr < xen_io_tlb_end) &&
+		!range_straddles_page_boundary(paddr, size) && !swiotlb_force) {
+		dma_mark_clean(vaddr, size);		
+		return;
+	}
+
 	/* NOTE: We use dev_addr here, not paddr! */
 	if (is_xen_swiotlb_buffer(dev_addr)) {
 		swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);
@@ -717,13 +828,36 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
 			 struct dma_attrs *attrs)
 {
 	struct scatterlist *sg;
-	int i;
+	int i, rc;
+	u64 dma_mask = DMA_BIT_MASK(32);
+	unsigned long flags;
 
 	BUG_ON(dir == DMA_NONE);
 
+	if (hwdev && hwdev->coherent_dma_mask)
+		dma_mask = dma_alloc_coherent_mask(hwdev, GFP_KERNEL);
+
 	for_each_sg(sgl, sg, nelems, i) {
 		phys_addr_t paddr = sg_phys(sg);
-		dma_addr_t dev_addr = xen_phys_to_bus_quick(paddr);
+		dma_addr_t dev_addr;
+
+		if (xen_feature(XENFEAT_auto_translated_physmap) &&
+			!range_straddles_page_boundary(paddr, sg->length) &&
+			sg->length <= PAGE_SIZE &&
+			!swiotlb_force) {
+
+			spin_lock_irqsave(&swiotlb_lock, flags);
+			rc = xen_pin_dev_page(hwdev, paddr, &dev_addr);
+			spin_unlock_irqrestore(&swiotlb_lock, flags);
+
+			if (!rc) {
+				dma_mark_clean(phys_to_virt(paddr), sg->length);
+				sg_dma_len(sg) = sg->length;
+				sg->dma_address = dev_addr;
+				continue;
+			}
+		}
+		dev_addr = xen_phys_to_bus_quick(paddr);
 
 		if (swiotlb_force ||
 		    xen_feature(XENFEAT_auto_translated_physmap) ||
-- 
1.7.2.5

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