[PATCH v2 0/7] Improve swiotlb performance by using physical addresses

[PATCH v2 0/7] Improve swiotlb performance by using physical addresses

[Alexander Duyck]

While working on 10Gb/s routing performance I found a significant amount of
time was being spent in the swiotlb DMA handler. Further digging found that a
significant amount of this was due to virtual to physical address translation
and calling the function that did it. It accounted for nearly 60% of the
total swiotlb overhead.

This patch set works to resolve that by replacing the io_tlb_start and
io_tlb_end virtual addresses with a physical addresses. In addition it changes
the io_tlb_overflow_buffer from a virtual to a physical address. I followed
through with the cleanup to the point that the only functions that really
require the virtual address for the DMA buffer are the init, free, and
bounce functions.

In the case of devices that are using the bounce buffers these patches should
result in only a slight performance gain if any. This is due to the locking
overhead required to map and unmap the buffers.

In the case of devices that are not making use of bounce buffers these patches
can significantly reduce their overhead. In the case of an ixgbe routing test
for example, these changes result in 7 fewer calls to __phys_addr and
allow is_swiotlb_buffer to become inlined due to a reduction in the number of
instructions. When running a routing throughput test using small packets I
saw roughly a 6% increase in packets rates after applying these patches. This
appears to match up with the CPU overhead reduction I was tracking via perf.

Before:
Results 10.0Mpps

After:
Results 10.6Mpps

Finally, I updated the parameter names for several of the core function calls
as there was some ambiguity in naming. Specifically virtual address pointers
were named dma_addr. When I changed these pointers to physical I instead used
the name tlb_addr as this value represented a physical address in the
io_tlb_start region and is less likely to be confused with a bus address.

v2:
I reviewed the changes and realized that the first patch that was dropping
io_tlb_end and calculating the value didn't actually gain me much once I had
gone through and translated the rest of the addresses to physical addresses.
As such I have updated the patch so that it instead is converting io_tlb_end
from a virtual address to a physical address.  This actually helps to reduce
the overhead for is_swiotlb_buffer and swiotlb_dma_supported by several
instructions.

---

Alexander Duyck (7):
      swiotlb:  Do not export swiotlb_bounce since there are no external consumers
      swiotlb: Use physical addresses instead of virtual in swiotlb_tbl_sync_single
      swiotlb: Use physical addresses for swiotlb_tbl_unmap_single
      swiotlb: Return physical addresses when calling swiotlb_tbl_map_single
      swiotlb: Make io_tlb_overflow_buffer a physical address
      swiotlb: Make io_tlb_start a physical address instead of a virtual one
      swiotlb: Make io_tlb_end a physical address instead of a virtual one


 drivers/xen/swiotlb-xen.c |   25 ++--
 include/linux/swiotlb.h   |   20 ++-
 lib/swiotlb.c             |  269 +++++++++++++++++++++++----------------------
 3 files changed, 163 insertions(+), 151 deletions(-)

-- 

[PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

[Alexander Duyck]

This change replaces all references to the virtual address for io_tlb_end
with references to the physical address io_tlb_end.  The main advantage of
replacing the virtual address with a physical address is that we can avoid
having to do multiple translations from the virtual address to the physical
one needed for testing an existing DMA address.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 lib/swiotlb.c |   24 +++++++++++++-----------
 1 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index f114bf6..19aac9f 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -57,7 +57,8 @@ int swiotlb_force;
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
  * API.
  */
-static char *io_tlb_start, *io_tlb_end;
+static char *io_tlb_start;
+phys_addr_t io_tlb_end;
 
 /*
  * The number of IO TLB blocks (in groups of 64) between io_tlb_start and
@@ -125,14 +126,16 @@ static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
 void swiotlb_print_info(void)
 {
 	unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
-	phys_addr_t pstart, pend;
+	phys_addr_t pstart;
+	unsigned char *vend;
 
 	pstart = virt_to_phys(io_tlb_start);
-	pend = virt_to_phys(io_tlb_end);
+	vend = phys_to_virt(io_tlb_end);
 
 	printk(KERN_INFO "software IO TLB [mem %#010llx-%#010llx] (%luMB) mapped at [%p-%p]\n",
-	       (unsigned long long)pstart, (unsigned long long)pend - 1,
-	       bytes >> 20, io_tlb_start, io_tlb_end - 1);
+	       (unsigned long long)pstart,
+	       (unsigned long long)io_tlb_end,
+	       bytes >> 20, io_tlb_start, vend - 1);
 }
 
 void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
@@ -143,7 +146,7 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 
 	io_tlb_nslabs = nslabs;
 	io_tlb_start = tlb;
-	io_tlb_end = io_tlb_start + bytes;
+	io_tlb_end = __pa(io_tlb_start) + bytes;
 
 	/*
 	 * Allocate and initialize the free list array.  This array is used
@@ -254,7 +257,7 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 
 	io_tlb_nslabs = nslabs;
 	io_tlb_start = tlb;
-	io_tlb_end = io_tlb_start + bytes;
+	io_tlb_end = virt_to_phys(io_tlb_start) + bytes;
 
 	memset(io_tlb_start, 0, bytes);
 
@@ -304,7 +307,7 @@ cleanup3:
 	                                                 sizeof(int)));
 	io_tlb_list = NULL;
 cleanup2:
-	io_tlb_end = NULL;
+	io_tlb_end = 0;
 	io_tlb_start = NULL;
 	io_tlb_nslabs = 0;
 	return -ENOMEM;
@@ -339,8 +342,7 @@ void __init swiotlb_free(void)
 
 static int is_swiotlb_buffer(phys_addr_t paddr)
 {
-	return paddr >= virt_to_phys(io_tlb_start) &&
-		paddr < virt_to_phys(io_tlb_end);
+	return paddr >= virt_to_phys(io_tlb_start) && paddr < io_tlb_end;
 }
 
 /*
@@ -938,6 +940,6 @@ EXPORT_SYMBOL(swiotlb_dma_mapping_error);
 int
 swiotlb_dma_supported(struct device *hwdev, u64 mask)
 {
-	return swiotlb_virt_to_bus(hwdev, io_tlb_end - 1) <= mask;
+	return phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
 }
 EXPORT_SYMBOL(swiotlb_dma_supported);

[PATCH v2 2/7] swiotlb: Make io_tlb_start a physical address instead of a virtual one

[Alexander Duyck]

This change replaces all references to the virtual address for io_tlb_start
with references to the physical address io_tlb_end.  The main advantage of
replacing the virtual address with a physical address is that we can avoid
having to do multiple translations from the virtual address to the physical
one needed for testing an existing DMA address.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 lib/swiotlb.c |   58 +++++++++++++++++++++++++++++----------------------------
 1 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 19aac9f..c492b84 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -57,8 +57,7 @@ int swiotlb_force;
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
  * API.
  */
-static char *io_tlb_start;
-phys_addr_t io_tlb_end;
+phys_addr_t io_tlb_start, io_tlb_end;
 
 /*
  * The number of IO TLB blocks (in groups of 64) between io_tlb_start and
@@ -126,16 +125,15 @@ static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
 void swiotlb_print_info(void)
 {
 	unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
-	phys_addr_t pstart;
-	unsigned char *vend;
+	unsigned char *vstart, *vend;
 
-	pstart = virt_to_phys(io_tlb_start);
+	vstart = phys_to_virt(io_tlb_start);
 	vend = phys_to_virt(io_tlb_end);
 
 	printk(KERN_INFO "software IO TLB [mem %#010llx-%#010llx] (%luMB) mapped at [%p-%p]\n",
-	       (unsigned long long)pstart,
+	       (unsigned long long)io_tlb_start,
 	       (unsigned long long)io_tlb_end,
-	       bytes >> 20, io_tlb_start, vend - 1);
+	       bytes >> 20, vstart, vend - 1);
 }
 
 void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
@@ -145,8 +143,8 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 	bytes = nslabs << IO_TLB_SHIFT;
 
 	io_tlb_nslabs = nslabs;
-	io_tlb_start = tlb;
-	io_tlb_end = __pa(io_tlb_start) + bytes;
+	io_tlb_start = __pa(tlb);
+	io_tlb_end = io_tlb_start + bytes;
 
 	/*
 	 * Allocate and initialize the free list array.  This array is used
@@ -176,6 +174,7 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 static void __init
 swiotlb_init_with_default_size(size_t default_size, int verbose)
 {
+	unsigned char *vstart;
 	unsigned long bytes;
 
 	if (!io_tlb_nslabs) {
@@ -188,11 +187,11 @@ swiotlb_init_with_default_size(size_t default_size, int verbose)
 	/*
 	 * Get IO TLB memory from the low pages
 	 */
-	io_tlb_start = alloc_bootmem_low_pages(PAGE_ALIGN(bytes));
-	if (!io_tlb_start)
+	vstart = alloc_bootmem_low_pages(PAGE_ALIGN(bytes));
+	if (!vstart)
 		panic("Cannot allocate SWIOTLB buffer");
 
-	swiotlb_init_with_tbl(io_tlb_start, io_tlb_nslabs, verbose);
+	swiotlb_init_with_tbl(vstart, io_tlb_nslabs, verbose);
 }
 
 void __init
@@ -210,6 +209,7 @@ int
 swiotlb_late_init_with_default_size(size_t default_size)
 {
 	unsigned long bytes, req_nslabs = io_tlb_nslabs;
+	unsigned char *vstart = NULL;
 	unsigned int order;
 	int rc = 0;
 
@@ -226,14 +226,14 @@ swiotlb_late_init_with_default_size(size_t default_size)
 	bytes = io_tlb_nslabs << IO_TLB_SHIFT;
 
 	while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
-		io_tlb_start = (void *)__get_free_pages(GFP_DMA | __GFP_NOWARN,
-							order);
-		if (io_tlb_start)
+		vstart = (void *)__get_free_pages(GFP_DMA | __GFP_NOWARN,
+						  order);
+		if (vstart)
 			break;
 		order--;
 	}
 
-	if (!io_tlb_start) {
+	if (!vstart) {
 		io_tlb_nslabs = req_nslabs;
 		return -ENOMEM;
 	}
@@ -242,9 +242,9 @@ swiotlb_late_init_with_default_size(size_t default_size)
 		       "for software IO TLB\n", (PAGE_SIZE << order) >> 20);
 		io_tlb_nslabs = SLABS_PER_PAGE << order;
 	}
-	rc = swiotlb_late_init_with_tbl(io_tlb_start, io_tlb_nslabs);
+	rc = swiotlb_late_init_with_tbl(vstart, io_tlb_nslabs);
 	if (rc)
-		free_pages((unsigned long)io_tlb_start, order);
+		free_pages((unsigned long)vstart, order);
 	return rc;
 }
 
@@ -256,10 +256,10 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	bytes = nslabs << IO_TLB_SHIFT;
 
 	io_tlb_nslabs = nslabs;
-	io_tlb_start = tlb;
-	io_tlb_end = virt_to_phys(io_tlb_start) + bytes;
+	io_tlb_start = virt_to_phys(tlb);
+	io_tlb_end = io_tlb_start + bytes;
 
-	memset(io_tlb_start, 0, bytes);
+	memset(tlb, 0, bytes);
 
 	/*
 	 * Allocate and initialize the free list array.  This array is used
@@ -308,7 +308,7 @@ cleanup3:
 	io_tlb_list = NULL;
 cleanup2:
 	io_tlb_end = 0;
-	io_tlb_start = NULL;
+	io_tlb_start = 0;
 	io_tlb_nslabs = 0;
 	return -ENOMEM;
 }
@@ -325,7 +325,7 @@ void __init swiotlb_free(void)
 			   get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
 		free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
 								 sizeof(int)));
-		free_pages((unsigned long)io_tlb_start,
+		free_pages((unsigned long)phys_to_virt(io_tlb_start),
 			   get_order(io_tlb_nslabs << IO_TLB_SHIFT));
 	} else {
 		free_bootmem_late(__pa(io_tlb_overflow_buffer),
@@ -334,7 +334,7 @@ void __init swiotlb_free(void)
 				  PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
 		free_bootmem_late(__pa(io_tlb_list),
 				  PAGE_ALIGN(io_tlb_nslabs * sizeof(int)));
-		free_bootmem_late(__pa(io_tlb_start),
+		free_bootmem_late(io_tlb_start,
 				  PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
 	}
 	io_tlb_nslabs = 0;
@@ -342,7 +342,7 @@ void __init swiotlb_free(void)
 
 static int is_swiotlb_buffer(phys_addr_t paddr)
 {
-	return paddr >= virt_to_phys(io_tlb_start) && paddr < io_tlb_end;
+	return paddr >= io_tlb_start && paddr < io_tlb_end;
 }
 
 /*
@@ -455,7 +455,7 @@ void *swiotlb_tbl_map_single(struct device *hwdev, dma_addr_t tbl_dma_addr,
 				io_tlb_list[i] = 0;
 			for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != IO_TLB_SEGSIZE - 1) && io_tlb_list[i]; i--)
 				io_tlb_list[i] = ++count;
-			dma_addr = io_tlb_start + (index << IO_TLB_SHIFT);
+			dma_addr = (char *)phys_to_virt(io_tlb_start) + (index << IO_TLB_SHIFT);
 
 			/*
 			 * Update the indices to avoid searching in the next
@@ -499,7 +499,7 @@ static void *
 map_single(struct device *hwdev, phys_addr_t phys, size_t size,
 	   enum dma_data_direction dir)
 {
-	dma_addr_t start_dma_addr = swiotlb_virt_to_bus(hwdev, io_tlb_start);
+	dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
 
 	return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size, dir);
 }
@@ -513,7 +513,7 @@ swiotlb_tbl_unmap_single(struct device *hwdev, char *dma_addr, size_t size,
 {
 	unsigned long flags;
 	int i, count, nslots = ALIGN(size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
-	int index = (dma_addr - io_tlb_start) >> IO_TLB_SHIFT;
+	int index = (dma_addr - (char *)phys_to_virt(io_tlb_start)) >> IO_TLB_SHIFT;
 	phys_addr_t phys = io_tlb_orig_addr[index];
 
 	/*
@@ -554,7 +554,7 @@ swiotlb_tbl_sync_single(struct device *hwdev, char *dma_addr, size_t size,
 			enum dma_data_direction dir,
 			enum dma_sync_target target)
 {
-	int index = (dma_addr - io_tlb_start) >> IO_TLB_SHIFT;
+	int index = (dma_addr - (char *)phys_to_virt(io_tlb_start)) >> IO_TLB_SHIFT;
 	phys_addr_t phys = io_tlb_orig_addr[index];
 
 	phys += ((unsigned long)dma_addr & ((1 << IO_TLB_SHIFT) - 1));

[PATCH v2 3/7] swiotlb: Make io_tlb_overflow_buffer a physical address

[Alexander Duyck]

This change makes it so that we can avoid virt_to_phys overhead when using the
io_tlb_overflow_buffer.  My original plan was to completely remove the value
and replace it with a constant but I had seen that there were recent patches
that stated this couldn't be done until all device drivers that depended on
that functionality be updated.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 lib/swiotlb.c |   61 ++++++++++++++++++++++++++++++++-------------------------
 1 files changed, 34 insertions(+), 27 deletions(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index c492b84..383f780 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -70,7 +70,7 @@ static unsigned long io_tlb_nslabs;
  */
 static unsigned long io_tlb_overflow = 32*1024;
 
-static void *io_tlb_overflow_buffer;
+phys_addr_t io_tlb_overflow_buffer;
 
 /*
  * This is a free list describing the number of free entries available from
@@ -138,6 +138,7 @@ void swiotlb_print_info(void)
 
 void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 {
+	void *v_overflow_buffer;
 	unsigned long i, bytes;
 
 	bytes = nslabs << IO_TLB_SHIFT;
@@ -147,6 +148,15 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 	io_tlb_end = io_tlb_start + bytes;
 
 	/*
+	 * Get the overflow emergency buffer
+	 */
+	v_overflow_buffer = alloc_bootmem_low_pages(PAGE_ALIGN(io_tlb_overflow));
+	if (!v_overflow_buffer)
+		panic("Cannot allocate SWIOTLB overflow buffer!\n");
+
+	io_tlb_overflow_buffer = __pa(v_overflow_buffer);
+
+	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
 	 * between io_tlb_start and io_tlb_end.
@@ -157,12 +167,6 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 	io_tlb_index = 0;
 	io_tlb_orig_addr = alloc_bootmem_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
 
-	/*
-	 * Get the overflow emergency buffer
-	 */
-	io_tlb_overflow_buffer = alloc_bootmem_low_pages(PAGE_ALIGN(io_tlb_overflow));
-	if (!io_tlb_overflow_buffer)
-		panic("Cannot allocate SWIOTLB overflow buffer!\n");
 	if (verbose)
 		swiotlb_print_info();
 }
@@ -252,6 +256,7 @@ int
 swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 {
 	unsigned long i, bytes;
+	unsigned char *v_overflow_buffer;
 
 	bytes = nslabs << IO_TLB_SHIFT;
 
@@ -262,6 +267,16 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	memset(tlb, 0, bytes);
 
 	/*
+	 * Get the overflow emergency buffer
+	 */
+	v_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
+						     get_order(io_tlb_overflow));
+	if (!v_overflow_buffer)
+		goto cleanup2;
+
+	io_tlb_overflow_buffer = virt_to_phys(v_overflow_buffer);
+
+	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
 	 * between io_tlb_start and io_tlb_end.
@@ -269,7 +284,7 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	io_tlb_list = (unsigned int *)__get_free_pages(GFP_KERNEL,
 	                              get_order(io_tlb_nslabs * sizeof(int)));
 	if (!io_tlb_list)
-		goto cleanup2;
+		goto cleanup3;
 
 	for (i = 0; i < io_tlb_nslabs; i++)
  		io_tlb_list[i] = IO_TLB_SEGSIZE - OFFSET(i, IO_TLB_SEGSIZE);
@@ -280,18 +295,10 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 				 get_order(io_tlb_nslabs *
 					   sizeof(phys_addr_t)));
 	if (!io_tlb_orig_addr)
-		goto cleanup3;
+		goto cleanup4;
 
 	memset(io_tlb_orig_addr, 0, io_tlb_nslabs * sizeof(phys_addr_t));
 
-	/*
-	 * Get the overflow emergency buffer
-	 */
-	io_tlb_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
-	                                          get_order(io_tlb_overflow));
-	if (!io_tlb_overflow_buffer)
-		goto cleanup4;
-
 	swiotlb_print_info();
 
 	late_alloc = 1;
@@ -299,13 +306,13 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	return 0;
 
 cleanup4:
-	free_pages((unsigned long)io_tlb_orig_addr,
-		   get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
-	io_tlb_orig_addr = NULL;
-cleanup3:
 	free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
 	                                                 sizeof(int)));
 	io_tlb_list = NULL;
+cleanup3:
+	free_pages((unsigned long)v_overflow_buffer,
+		   get_order(io_tlb_overflow));
+	io_tlb_overflow_buffer = 0;
 cleanup2:
 	io_tlb_end = 0;
 	io_tlb_start = 0;
@@ -315,11 +322,11 @@ cleanup2:
 
 void __init swiotlb_free(void)
 {
-	if (!io_tlb_overflow_buffer)
+	if (!io_tlb_orig_addr)
 		return;
 
 	if (late_alloc) {
-		free_pages((unsigned long)io_tlb_overflow_buffer,
+		free_pages((unsigned long)phys_to_virt(io_tlb_overflow_buffer),
 			   get_order(io_tlb_overflow));
 		free_pages((unsigned long)io_tlb_orig_addr,
 			   get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
@@ -328,7 +335,7 @@ void __init swiotlb_free(void)
 		free_pages((unsigned long)phys_to_virt(io_tlb_start),
 			   get_order(io_tlb_nslabs << IO_TLB_SHIFT));
 	} else {
-		free_bootmem_late(__pa(io_tlb_overflow_buffer),
+		free_bootmem_late(io_tlb_overflow_buffer,
 				  PAGE_ALIGN(io_tlb_overflow));
 		free_bootmem_late(__pa(io_tlb_orig_addr),
 				  PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
@@ -698,7 +705,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	map = map_single(dev, phys, size, dir);
 	if (!map) {
 		swiotlb_full(dev, size, dir, 1);
-		map = io_tlb_overflow_buffer;
+		return phys_to_dma(dev, io_tlb_overflow_buffer);
 	}
 
 	dev_addr = swiotlb_virt_to_bus(dev, map);
@@ -708,7 +715,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	 */
 	if (!dma_capable(dev, dev_addr, size)) {
 		swiotlb_tbl_unmap_single(dev, map, size, dir);
-		dev_addr = swiotlb_virt_to_bus(dev, io_tlb_overflow_buffer);
+		return phys_to_dma(dev, io_tlb_overflow_buffer);
 	}
 
 	return dev_addr;
@@ -927,7 +934,7 @@ EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
 int
 swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
 {
-	return (dma_addr == swiotlb_virt_to_bus(hwdev, io_tlb_overflow_buffer));
+	return (dma_addr == phys_to_dma(hwdev, io_tlb_overflow_buffer));
 }
 EXPORT_SYMBOL(swiotlb_dma_mapping_error);
 

[PATCH v2 4/7] swiotlb: Return physical addresses when calling swiotlb_tbl_map_single

[Alexander Duyck]

This change makes it so that swiotlb_tbl_map_single will return a physical
address instead of a virtual address when called.  The advantage to this once
again is that we are avoiding a number of virt_to_phys and phys_to_virt
translations by working with everything as a physical address.

One change I had to make in order to support using physical addresses is that
I could no longer trust 0 to be a invalid physical address on all platforms.
So instead I made it so that ~0 is returned on error.  This should never be a
valid return value as it implies that only one byte would be available for
use.

In order to clarify things since we now have 2 physical addresses in use
inside of swiotlb_tbl_map_single I am renaming phys to orig_addr, and
dma_addr to tlb_addr.  This way is should be clear that orig_addr is
contained within io_orig_addr and tlb_addr is an address within the
io_tlb_addr buffer.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 drivers/xen/swiotlb-xen.c |   22 ++++++-------
 include/linux/swiotlb.h   |   11 +++++-
 lib/swiotlb.c             |   78 +++++++++++++++++++++++----------------------
 3 files changed, 59 insertions(+), 52 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 58db6df..8a6035a 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -338,9 +338,8 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 				enum dma_data_direction dir,
 				struct dma_attrs *attrs)
 {
-	phys_addr_t phys = page_to_phys(page) + offset;
+	phys_addr_t map, phys = page_to_phys(page) + offset;
 	dma_addr_t dev_addr = xen_phys_to_bus(phys);
-	void *map;
 
 	BUG_ON(dir == DMA_NONE);
 	/*
@@ -356,16 +355,16 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 	 * Oh well, have to allocate and map a bounce buffer.
 	 */
 	map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir);
-	if (!map)
+	if (map == SWIOTLB_MAP_ERROR)
 		return DMA_ERROR_CODE;
 
-	dev_addr = xen_virt_to_bus(map);
+	dev_addr = xen_phys_to_bus(map);
 
 	/*
 	 * Ensure that the address returned is DMA'ble
 	 */
 	if (!dma_capable(dev, dev_addr, size)) {
-		swiotlb_tbl_unmap_single(dev, map, size, dir);
+		swiotlb_tbl_unmap_single(dev, phys_to_virt(map), size, dir);
 		dev_addr = 0;
 	}
 	return dev_addr;
@@ -494,11 +493,12 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
 		if (swiotlb_force ||
 		    !dma_capable(hwdev, dev_addr, sg->length) ||
 		    range_straddles_page_boundary(paddr, sg->length)) {
-			void *map = swiotlb_tbl_map_single(hwdev,
-							   start_dma_addr,
-							   sg_phys(sg),
-							   sg->length, dir);
-			if (!map) {
+			phys_addr_t map = swiotlb_tbl_map_single(hwdev,
+								 start_dma_addr,
+								 sg_phys(sg),
+								 sg->length,
+								 dir);
+			if (map == SWIOTLB_MAP_ERROR) {
 				/* Don't panic here, we expect map_sg users
 				   to do proper error handling. */
 				xen_swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
@@ -506,7 +506,7 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
 				sgl[0].dma_length = 0;
 				return DMA_ERROR_CODE;
 			}
-			sg->dma_address = xen_virt_to_bus(map);
+			sg->dma_address = xen_phys_to_bus(map);
 		} else
 			sg->dma_address = dev_addr;
 		sg->dma_length = sg->length;
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 8d08b3e..1995f3e 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -34,9 +34,14 @@ enum dma_sync_target {
 	SYNC_FOR_CPU = 0,
 	SYNC_FOR_DEVICE = 1,
 };
-extern void *swiotlb_tbl_map_single(struct device *hwdev, dma_addr_t tbl_dma_addr,
-				    phys_addr_t phys, size_t size,
-				    enum dma_data_direction dir);
+
+/* define the last possible byte of physical address space as a mapping error */
+#define SWIOTLB_MAP_ERROR (~(phys_addr_t)0x0)
+
+extern phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
+					  dma_addr_t tbl_dma_addr,
+					  phys_addr_t phys, size_t size,
+					  enum dma_data_direction dir);
 
 extern void swiotlb_tbl_unmap_single(struct device *hwdev, char *dma_addr,
 				     size_t size, enum dma_data_direction dir);
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 383f780..58d0bbd 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -393,12 +393,13 @@ void swiotlb_bounce(phys_addr_t phys, char *dma_addr, size_t size,
 }
 EXPORT_SYMBOL_GPL(swiotlb_bounce);
 
-void *swiotlb_tbl_map_single(struct device *hwdev, dma_addr_t tbl_dma_addr,
-			     phys_addr_t phys, size_t size,
-			     enum dma_data_direction dir)
+phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
+				   dma_addr_t tbl_dma_addr,
+				   phys_addr_t orig_addr, size_t size,
+				   enum dma_data_direction dir)
 {
 	unsigned long flags;
-	char *dma_addr;
+	phys_addr_t tlb_addr;
 	unsigned int nslots, stride, index, wrap;
 	int i;
 	unsigned long mask;
@@ -462,7 +463,7 @@ void *swiotlb_tbl_map_single(struct device *hwdev, dma_addr_t tbl_dma_addr,
 				io_tlb_list[i] = 0;
 			for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != IO_TLB_SEGSIZE - 1) && io_tlb_list[i]; i--)
 				io_tlb_list[i] = ++count;
-			dma_addr = (char *)phys_to_virt(io_tlb_start) + (index << IO_TLB_SHIFT);
+			tlb_addr = io_tlb_start + (index << IO_TLB_SHIFT);
 
 			/*
 			 * Update the indices to avoid searching in the next
@@ -480,7 +481,7 @@ void *swiotlb_tbl_map_single(struct device *hwdev, dma_addr_t tbl_dma_addr,
 
 not_found:
 	spin_unlock_irqrestore(&io_tlb_lock, flags);
-	return NULL;
+	return SWIOTLB_MAP_ERROR;
 found:
 	spin_unlock_irqrestore(&io_tlb_lock, flags);
 
@@ -490,11 +491,12 @@ found:
 	 * needed.
 	 */
 	for (i = 0; i < nslots; i++)
-		io_tlb_orig_addr[index+i] = phys + (i << IO_TLB_SHIFT);
+		io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
 	if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
-		swiotlb_bounce(phys, dma_addr, size, DMA_TO_DEVICE);
+		swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr), size,
+			       DMA_TO_DEVICE);
 
-	return dma_addr;
+	return tlb_addr;
 }
 EXPORT_SYMBOL_GPL(swiotlb_tbl_map_single);
 
@@ -502,9 +504,8 @@ EXPORT_SYMBOL_GPL(swiotlb_tbl_map_single);
  * Allocates bounce buffer and returns its kernel virtual address.
  */
 
-static void *
-map_single(struct device *hwdev, phys_addr_t phys, size_t size,
-	   enum dma_data_direction dir)
+phys_addr_t map_single(struct device *hwdev, phys_addr_t phys, size_t size,
+		       enum dma_data_direction dir)
 {
 	dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
 
@@ -598,12 +599,15 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 		dma_mask = hwdev->coherent_dma_mask;
 
 	ret = (void *)__get_free_pages(flags, order);
-	if (ret && swiotlb_virt_to_bus(hwdev, ret) + size - 1 > dma_mask) {
-		/*
-		 * The allocated memory isn't reachable by the device.
-		 */
-		free_pages((unsigned long) ret, order);
-		ret = NULL;
+	if (ret) {
+		dev_addr = swiotlb_virt_to_bus(hwdev, ret);
+		if (dev_addr + size - 1 > dma_mask) {
+			/*
+			 * The allocated memory isn't reachable by the device.
+			 */
+			free_pages((unsigned long) ret, order);
+			ret = NULL;
+		}
 	}
 	if (!ret) {
 		/*
@@ -611,13 +615,13 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 		 * GFP_DMA memory; fall back on map_single(), which
 		 * will grab memory from the lowest available address range.
 		 */
-		ret = map_single(hwdev, 0, size, DMA_FROM_DEVICE);
-		if (!ret)
+		phys_addr_t paddr = map_single(hwdev, 0, size, DMA_FROM_DEVICE);
+		if (paddr == SWIOTLB_MAP_ERROR)
 			return NULL;
-	}
 
-	memset(ret, 0, size);
-	dev_addr = swiotlb_virt_to_bus(hwdev, ret);
+		ret = phys_to_virt(paddr);
+		dev_addr = phys_to_dma(hwdev, paddr);
+	}
 
 	/* Confirm address can be DMA'd by device */
 	if (dev_addr + size - 1 > dma_mask) {
@@ -629,7 +633,10 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 		swiotlb_tbl_unmap_single(hwdev, ret, size, DMA_TO_DEVICE);
 		return NULL;
 	}
+
 	*dma_handle = dev_addr;
+	memset(ret, 0, size);
+
 	return ret;
 }
 EXPORT_SYMBOL(swiotlb_alloc_coherent);
@@ -686,9 +693,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 			    enum dma_data_direction dir,
 			    struct dma_attrs *attrs)
 {
-	phys_addr_t phys = page_to_phys(page) + offset;
+	phys_addr_t map, phys = page_to_phys(page) + offset;
 	dma_addr_t dev_addr = phys_to_dma(dev, phys);
-	void *map;
 
 	BUG_ON(dir == DMA_NONE);
 	/*
@@ -699,22 +705,18 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 	if (dma_capable(dev, dev_addr, size) && !swiotlb_force)
 		return dev_addr;
 
-	/*
-	 * Oh well, have to allocate and map a bounce buffer.
-	 */
+	/* Oh well, have to allocate and map a bounce buffer. */
 	map = map_single(dev, phys, size, dir);
-	if (!map) {
+	if (map == SWIOTLB_MAP_ERROR) {
 		swiotlb_full(dev, size, dir, 1);
 		return phys_to_dma(dev, io_tlb_overflow_buffer);
 	}
 
-	dev_addr = swiotlb_virt_to_bus(dev, map);
+	dev_addr = phys_to_dma(dev, map);
 
-	/*
-	 * Ensure that the address returned is DMA'ble
-	 */
+	/* Ensure that the address returned is DMA'ble */
 	if (!dma_capable(dev, dev_addr, size)) {
-		swiotlb_tbl_unmap_single(dev, map, size, dir);
+		swiotlb_tbl_unmap_single(dev, phys_to_virt(map), size, dir);
 		return phys_to_dma(dev, io_tlb_overflow_buffer);
 	}
 
@@ -840,9 +842,9 @@ swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems,
 
 		if (swiotlb_force ||
 		    !dma_capable(hwdev, dev_addr, sg->length)) {
-			void *map = map_single(hwdev, sg_phys(sg),
-					       sg->length, dir);
-			if (!map) {
+			phys_addr_t map = map_single(hwdev, sg_phys(sg),
+						     sg->length, dir);
+			if (map == SWIOTLB_MAP_ERROR) {
 				/* Don't panic here, we expect map_sg users
 				   to do proper error handling. */
 				swiotlb_full(hwdev, sg->length, dir, 0);
@@ -851,7 +853,7 @@ swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems,
 				sgl[0].dma_length = 0;
 				return 0;
 			}
-			sg->dma_address = swiotlb_virt_to_bus(hwdev, map);
+			sg->dma_address = phys_to_dma(hwdev, map);
 		} else
 			sg->dma_address = dev_addr;
 		sg->dma_length = sg->length;

[PATCH v2 5/7] swiotlb: Use physical addresses for swiotlb_tbl_unmap_single

[Alexander Duyck]

This change makes it so that the unmap functionality also uses physical
addresses.  This helps to further reduce the use of virt_to_phys and
phys_to_virt functions.

In order to clarify things since we now have 2 physical addresses in use
inside of swiotlb_tbl_unmap_single I am renaming phys to orig_addr, and
dma_addr to tlb_addr.  This way is should be clear that orig_addr is
contained within io_orig_addr and tlb_addr is an address within the
io_tlb_addr buffer.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 drivers/xen/swiotlb-xen.c |    4 ++--
 include/linux/swiotlb.h   |    3 ++-
 lib/swiotlb.c             |   37 +++++++++++++++++++------------------
 3 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 8a6035a..4cedc28 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -364,7 +364,7 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 	 * Ensure that the address returned is DMA'ble
 	 */
 	if (!dma_capable(dev, dev_addr, size)) {
-		swiotlb_tbl_unmap_single(dev, phys_to_virt(map), size, dir);
+		swiotlb_tbl_unmap_single(dev, map, size, dir);
 		dev_addr = 0;
 	}
 	return dev_addr;
@@ -388,7 +388,7 @@ static void xen_unmap_single(struct device *hwdev, dma_addr_t dev_addr,
 
 	/* NOTE: We use dev_addr here, not paddr! */
 	if (is_xen_swiotlb_buffer(dev_addr)) {
-		swiotlb_tbl_unmap_single(hwdev, phys_to_virt(paddr), size, dir);
+		swiotlb_tbl_unmap_single(hwdev, paddr, size, dir);
 		return;
 	}
 
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 1995f3e..291643c 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -43,7 +43,8 @@ extern phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 					  phys_addr_t phys, size_t size,
 					  enum dma_data_direction dir);
 
-extern void swiotlb_tbl_unmap_single(struct device *hwdev, char *dma_addr,
+extern void swiotlb_tbl_unmap_single(struct device *hwdev,
+				     phys_addr_t tlb_addr,
 				     size_t size, enum dma_data_direction dir);
 
 extern void swiotlb_tbl_sync_single(struct device *hwdev, char *dma_addr,
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 58d0bbd..e0e66db 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -515,20 +515,20 @@ phys_addr_t map_single(struct device *hwdev, phys_addr_t phys, size_t size,
 /*
  * dma_addr is the kernel virtual address of the bounce buffer to unmap.
  */
-void
-swiotlb_tbl_unmap_single(struct device *hwdev, char *dma_addr, size_t size,
-			enum dma_data_direction dir)
+void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
+			      size_t size, enum dma_data_direction dir)
 {
 	unsigned long flags;
 	int i, count, nslots = ALIGN(size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
-	int index = (dma_addr - (char *)phys_to_virt(io_tlb_start)) >> IO_TLB_SHIFT;
-	phys_addr_t phys = io_tlb_orig_addr[index];
+	int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT;
+	phys_addr_t orig_addr = io_tlb_orig_addr[index];
 
 	/*
 	 * First, sync the memory before unmapping the entry
 	 */
 	if (phys && ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL)))
-		swiotlb_bounce(phys, dma_addr, size, DMA_FROM_DEVICE);
+		swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr),
+			       size, DMA_FROM_DEVICE);
 
 	/*
 	 * Return the buffer to the free list by setting the corresponding
@@ -621,17 +621,18 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 
 		ret = phys_to_virt(paddr);
 		dev_addr = phys_to_dma(hwdev, paddr);
-	}
 
-	/* Confirm address can be DMA'd by device */
-	if (dev_addr + size - 1 > dma_mask) {
-		printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
-		       (unsigned long long)dma_mask,
-		       (unsigned long long)dev_addr);
+		/* Confirm address can be DMA'd by device */
+		if (dev_addr + size - 1 > dma_mask) {
+			printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
+			       (unsigned long long)dma_mask,
+			       (unsigned long long)dev_addr);
 
-		/* DMA_TO_DEVICE to avoid memcpy in unmap_single */
-		swiotlb_tbl_unmap_single(hwdev, ret, size, DMA_TO_DEVICE);
-		return NULL;
+			/* DMA_TO_DEVICE to avoid memcpy in unmap_single */
+			swiotlb_tbl_unmap_single(hwdev, paddr,
+						 size, DMA_TO_DEVICE);
+			return NULL;
+		}
 	}
 
 	*dma_handle = dev_addr;
@@ -652,7 +653,7 @@ swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 		free_pages((unsigned long)vaddr, get_order(size));
 	else
 		/* DMA_TO_DEVICE to avoid memcpy in swiotlb_tbl_unmap_single */
-		swiotlb_tbl_unmap_single(hwdev, vaddr, size, DMA_TO_DEVICE);
+		swiotlb_tbl_unmap_single(hwdev, paddr, size, DMA_TO_DEVICE);
 }
 EXPORT_SYMBOL(swiotlb_free_coherent);
 
@@ -716,7 +717,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
 
 	/* Ensure that the address returned is DMA'ble */
 	if (!dma_capable(dev, dev_addr, size)) {
-		swiotlb_tbl_unmap_single(dev, phys_to_virt(map), size, dir);
+		swiotlb_tbl_unmap_single(dev, map, size, dir);
 		return phys_to_dma(dev, io_tlb_overflow_buffer);
 	}
 
@@ -740,7 +741,7 @@ static void unmap_single(struct device *hwdev, dma_addr_t dev_addr,
 	BUG_ON(dir == DMA_NONE);
 
 	if (is_swiotlb_buffer(paddr)) {
-		swiotlb_tbl_unmap_single(hwdev, phys_to_virt(paddr), size, dir);
+		swiotlb_tbl_unmap_single(hwdev, paddr, size, dir);
 		return;
 	}
 

[PATCH v2 6/7] swiotlb: Use physical addresses instead of virtual in swiotlb_tbl_sync_single

[Alexander Duyck]

This change makes it so that the sync functionality also uses physical
addresses.  This helps to further reduce the use of virt_to_phys and
phys_to_virt functions.

In order to clarify things since we now have 2 physical addresses in use
inside of swiotlb_tbl_sync_single I am renaming phys to orig_addr, and
dma_addr to tlb_addr.  This way is should be clear that orig_addr is
contained within io_orig_addr and tlb_addr is an address within the
io_tlb_addr buffer.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 drivers/xen/swiotlb-xen.c |    3 +--
 include/linux/swiotlb.h   |    3 ++-
 lib/swiotlb.c             |   22 +++++++++++-----------
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 4cedc28..af47e75 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -433,8 +433,7 @@ xen_swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
 
 	/* NOTE: We use dev_addr here, not paddr! */
 	if (is_xen_swiotlb_buffer(dev_addr)) {
-		swiotlb_tbl_sync_single(hwdev, phys_to_virt(paddr), size, dir,
-				       target);
+		swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);
 		return;
 	}
 
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 291643c..e0ac98f 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -47,7 +47,8 @@ extern void swiotlb_tbl_unmap_single(struct device *hwdev,
 				     phys_addr_t tlb_addr,
 				     size_t size, enum dma_data_direction dir);
 
-extern void swiotlb_tbl_sync_single(struct device *hwdev, char *dma_addr,
+extern void swiotlb_tbl_sync_single(struct device *hwdev,
+				    phys_addr_t tlb_addr,
 				    size_t size, enum dma_data_direction dir,
 				    enum dma_sync_target target);
 
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index e0e66db..a81138f 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -557,26 +557,27 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
 }
 EXPORT_SYMBOL_GPL(swiotlb_tbl_unmap_single);
 
-void
-swiotlb_tbl_sync_single(struct device *hwdev, char *dma_addr, size_t size,
-			enum dma_data_direction dir,
-			enum dma_sync_target target)
+void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
+			     size_t size, enum dma_data_direction dir,
+			     enum dma_sync_target target)
 {
-	int index = (dma_addr - (char *)phys_to_virt(io_tlb_start)) >> IO_TLB_SHIFT;
-	phys_addr_t phys = io_tlb_orig_addr[index];
+	int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT;
+	phys_addr_t orig_addr = io_tlb_orig_addr[index];
 
-	phys += ((unsigned long)dma_addr & ((1 << IO_TLB_SHIFT) - 1));
+	orig_addr += (unsigned long)tlb_addr & ((1 << IO_TLB_SHIFT) - 1);
 
 	switch (target) {
 	case SYNC_FOR_CPU:
 		if (likely(dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL))
-			swiotlb_bounce(phys, dma_addr, size, DMA_FROM_DEVICE);
+			swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr),
+				       size, DMA_FROM_DEVICE);
 		else
 			BUG_ON(dir != DMA_TO_DEVICE);
 		break;
 	case SYNC_FOR_DEVICE:
 		if (likely(dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
-			swiotlb_bounce(phys, dma_addr, size, DMA_TO_DEVICE);
+			swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr),
+				       size, DMA_TO_DEVICE);
 		else
 			BUG_ON(dir != DMA_FROM_DEVICE);
 		break;
@@ -785,8 +786,7 @@ swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
 	BUG_ON(dir == DMA_NONE);
 
 	if (is_swiotlb_buffer(paddr)) {
-		swiotlb_tbl_sync_single(hwdev, phys_to_virt(paddr), size, dir,
-				       target);
+		swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);
 		return;
 	}
 

[PATCH v2 7/7] swiotlb: Do not export swiotlb_bounce since there are no external consumers

[Alexander Duyck]

Currently swiotlb is the only consumer for swiotlb_bounce.  Since that is the
case it doesn't make much sense to be exporting it so make it a static
function only.

In addition we can save a few more lines of code by making it so that it
accepts the DMA address as a physical address instead of a virtual one.  This
is the last piece in essentially pushing all of the DMA address values to use
physical addresses in swiotlb.

In order to clarify things since we now have 2 physical addresses in use
inside of swiotlb_bounce I am renaming phys to orig_addr, and dma_addr to
tlb_addr.  This way is should be clear that orig_addr is contained within
io_orig_addr and tlb_addr is an address within the io_tlb_addr buffer.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

 include/linux/swiotlb.h |    3 ---
 lib/swiotlb.c           |   35 ++++++++++++++++-------------------
 2 files changed, 16 insertions(+), 22 deletions(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index e0ac98f..071d62c 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -53,9 +53,6 @@ extern void swiotlb_tbl_sync_single(struct device *hwdev,
 				    enum dma_sync_target target);
 
 /* Accessory functions. */
-extern void swiotlb_bounce(phys_addr_t phys, char *dma_addr, size_t size,
-			   enum dma_data_direction dir);
-
 extern void
 *swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 			dma_addr_t *dma_handle, gfp_t flags);
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index a81138f..fc31bdf 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -355,14 +355,15 @@ static int is_swiotlb_buffer(phys_addr_t paddr)
 /*
  * Bounce: copy the swiotlb buffer back to the original dma location
  */
-void swiotlb_bounce(phys_addr_t phys, char *dma_addr, size_t size,
-		    enum dma_data_direction dir)
+static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr,
+			   size_t size, enum dma_data_direction dir)
 {
-	unsigned long pfn = PFN_DOWN(phys);
+	unsigned long pfn = PFN_DOWN(orig_addr);
+	unsigned char *vaddr = phys_to_virt(tlb_addr);
 
 	if (PageHighMem(pfn_to_page(pfn))) {
 		/* The buffer does not have a mapping.  Map it in and copy */
-		unsigned int offset = phys & ~PAGE_MASK;
+		unsigned int offset = orig_addr & ~PAGE_MASK;
 		char *buffer;
 		unsigned int sz = 0;
 		unsigned long flags;
@@ -373,25 +374,23 @@ void swiotlb_bounce(phys_addr_t phys, char *dma_addr, size_t size,
 			local_irq_save(flags);
 			buffer = kmap_atomic(pfn_to_page(pfn));
 			if (dir == DMA_TO_DEVICE)
-				memcpy(dma_addr, buffer + offset, sz);
+				memcpy(vaddr, buffer + offset, sz);
 			else
-				memcpy(buffer + offset, dma_addr, sz);
+				memcpy(buffer + offset, vaddr, sz);
 			kunmap_atomic(buffer);
 			local_irq_restore(flags);
 
 			size -= sz;
 			pfn++;
-			dma_addr += sz;
+			vaddr += sz;
 			offset = 0;
 		}
+	} else if (dir == DMA_TO_DEVICE) {
+		memcpy(vaddr, phys_to_virt(orig_addr), size);
 	} else {
-		if (dir == DMA_TO_DEVICE)
-			memcpy(dma_addr, phys_to_virt(phys), size);
-		else
-			memcpy(phys_to_virt(phys), dma_addr, size);
+		memcpy(phys_to_virt(orig_addr), vaddr, size);
 	}
 }
-EXPORT_SYMBOL_GPL(swiotlb_bounce);
 
 phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 				   dma_addr_t tbl_dma_addr,
@@ -493,8 +492,7 @@ found:
 	for (i = 0; i < nslots; i++)
 		io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
 	if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
-		swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr), size,
-			       DMA_TO_DEVICE);
+		swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE);
 
 	return tlb_addr;
 }
@@ -526,9 +524,8 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
 	/*
 	 * First, sync the memory before unmapping the entry
 	 */
-	if (phys && ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL)))
-		swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr),
-			       size, DMA_FROM_DEVICE);
+	if (orig_addr && ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL)))
+		swiotlb_bounce(orig_addr, tlb_addr, size, DMA_FROM_DEVICE);
 
 	/*
 	 * Return the buffer to the free list by setting the corresponding
@@ -569,14 +566,14 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
 	switch (target) {
 	case SYNC_FOR_CPU:
 		if (likely(dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL))
-			swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr),
+			swiotlb_bounce(orig_addr, tlb_addr,
 				       size, DMA_FROM_DEVICE);
 		else
 			BUG_ON(dir != DMA_TO_DEVICE);
 		break;
 	case SYNC_FOR_DEVICE:
 		if (likely(dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
-			swiotlb_bounce(orig_addr, phys_to_virt(tlb_addr),
+			swiotlb_bounce(orig_addr, tlb_addr,
 				       size, DMA_TO_DEVICE);
 		else
 			BUG_ON(dir != DMA_FROM_DEVICE);

Re: [PATCH v2 0/7] Improve swiotlb performance by using physical addresses

[Alexander Duyck]

On 10/11/2012 01:34 PM, Alexander Duyck wrote:
> While working on 10Gb/s routing performance I found a significant amount of
> time was being spent in the swiotlb DMA handler. Further digging found that a
> significant amount of this was due to virtual to physical address translation
> and calling the function that did it. It accounted for nearly 60% of the
> total swiotlb overhead.
>
> This patch set works to resolve that by replacing the io_tlb_start and
> io_tlb_end virtual addresses with a physical addresses. In addition it changes
> the io_tlb_overflow_buffer from a virtual to a physical address. I followed
> through with the cleanup to the point that the only functions that really
> require the virtual address for the DMA buffer are the init, free, and
> bounce functions.
>
> In the case of devices that are using the bounce buffers these patches should
> result in only a slight performance gain if any. This is due to the locking
> overhead required to map and unmap the buffers.
>
> In the case of devices that are not making use of bounce buffers these patches
> can significantly reduce their overhead. In the case of an ixgbe routing test
> for example, these changes result in 7 fewer calls to __phys_addr and
> allow is_swiotlb_buffer to become inlined due to a reduction in the number of
> instructions. When running a routing throughput test using small packets I
> saw roughly a 6% increase in packets rates after applying these patches. This
> appears to match up with the CPU overhead reduction I was tracking via perf.
>
> Before:
> Results 10.0Mpps
>
> After:
> Results 10.6Mpps
>
> Finally, I updated the parameter names for several of the core function calls
> as there was some ambiguity in naming. Specifically virtual address pointers
> were named dma_addr. When I changed these pointers to physical I instead used
> the name tlb_addr as this value represented a physical address in the
> io_tlb_start region and is less likely to be confused with a bus address.
>
> v2:
> I reviewed the changes and realized that the first patch that was dropping
> io_tlb_end and calculating the value didn't actually gain me much once I had
> gone through and translated the rest of the addresses to physical addresses.
> As such I have updated the patch so that it instead is converting io_tlb_end
> from a virtual address to a physical address.  This actually helps to reduce
> the overhead for is_swiotlb_buffer and swiotlb_dma_supported by several
> instructions.

The first three patches were replacing "static char *" with
"phys_addr_t" when I should have been using "static phys_addr_t".  As
such I will submit an updated v3 version on Monday.

Thanks,

Alex

Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

[Hillf Danton]

Hi Alexander,

On Fri, Oct 12, 2012 at 4:34 AM, Alexander Duyck
<alexander.h.duyck@intel.com> wrote:
> This change replaces all references to the virtual address for io_tlb_end
> with references to the physical address io_tlb_end.  The main advantage of
> replacing the virtual address with a physical address is that we can avoid
> having to do multiple translations from the virtual address to the physical
> one needed for testing an existing DMA address.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> ---
>
>  lib/swiotlb.c |   24 +++++++++++++-----------
>  1 files changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index f114bf6..19aac9f 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -57,7 +57,8 @@ int swiotlb_force;
>   * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
>   * API.
>   */
> -static char *io_tlb_start, *io_tlb_end;
> +static char *io_tlb_start;
> +phys_addr_t io_tlb_end;

If add io_tlb_start_phy and io_tlb_end_phy, could we get same results
with less hunks?

Hillf

Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

[Alexander Duyck]

On 10/13/2012 05:52 AM, Hillf Danton wrote:
> Hi Alexander,
>
> On Fri, Oct 12, 2012 at 4:34 AM, Alexander Duyck
> <alexander.h.duyck@intel.com> wrote:
>> This change replaces all references to the virtual address for io_tlb_end
>> with references to the physical address io_tlb_end.  The main advantage of
>> replacing the virtual address with a physical address is that we can avoid
>> having to do multiple translations from the virtual address to the physical
>> one needed for testing an existing DMA address.
>>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
>> ---
>>
>>  lib/swiotlb.c |   24 +++++++++++++-----------
>>  1 files changed, 13 insertions(+), 11 deletions(-)
>>
>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
>> index f114bf6..19aac9f 100644
>> --- a/lib/swiotlb.c
>> +++ b/lib/swiotlb.c
>> @@ -57,7 +57,8 @@ int swiotlb_force;
>>   * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
>>   * API.
>>   */
>> -static char *io_tlb_start, *io_tlb_end;
>> +static char *io_tlb_start;
>> +phys_addr_t io_tlb_end;
> If add io_tlb_start_phy and io_tlb_end_phy, could we get same results
> with less hunks?
>
> Hillf

What do you mean by less hunks?  Are you referring to the memory space? 
If so, then the patches I am submitting do not impact how much space is
used for the bounce buffer.  The only real result of these patches is
that the total code path is significantly reduced since we don't have to
perform any virtual to physical translations in the hot-path.

Thanks,

Alex

Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

[Konrad Rzeszutek Wilk]

On Mon, Oct 15, 2012 at 08:43:28AM -0700, Alexander Duyck wrote:
> On 10/13/2012 05:52 AM, Hillf Danton wrote:
> > Hi Alexander,
> >
> > On Fri, Oct 12, 2012 at 4:34 AM, Alexander Duyck
> > <alexander.h.duyck@intel.com> wrote:
> >> This change replaces all references to the virtual address for io_tlb_end
> >> with references to the physical address io_tlb_end.  The main advantage of
> >> replacing the virtual address with a physical address is that we can avoid
> >> having to do multiple translations from the virtual address to the physical
> >> one needed for testing an existing DMA address.
> >>
> >> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> >> ---
> >>
> >>  lib/swiotlb.c |   24 +++++++++++++-----------
> >>  1 files changed, 13 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> >> index f114bf6..19aac9f 100644
> >> --- a/lib/swiotlb.c
> >> +++ b/lib/swiotlb.c
> >> @@ -57,7 +57,8 @@ int swiotlb_force;
> >>   * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
> >>   * API.
> >>   */
> >> -static char *io_tlb_start, *io_tlb_end;
> >> +static char *io_tlb_start;
> >> +phys_addr_t io_tlb_end;
> > If add io_tlb_start_phy and io_tlb_end_phy, could we get same results
> > with less hunks?
> >
> > Hillf
> 
> What do you mean by less hunks?  Are you referring to the memory space? 

As in less patch movements.
> If so, then the patches I am submitting do not impact how much space is
> used for the bounce buffer.  The only real result of these patches is
> that the total code path is significantly reduced since we don't have to
> perform any virtual to physical translations in the hot-path.

No. He is referring that you can keep io_tlb_end still here. Just
do the computation of the physical address in the init path (of the end).
Then you don't need to do the shifting in the 'is-this-swiotlb-buffer'
and can just do a simple:
	if (dma_addr >= io_tlb_start && dma_addr <= io_tlb_end)

Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

[Alexander Duyck]

On 10/18/2012 05:41 AM, Konrad Rzeszutek Wilk wrote:
> On Mon, Oct 15, 2012 at 08:43:28AM -0700, Alexander Duyck wrote:
>> On 10/13/2012 05:52 AM, Hillf Danton wrote:
>>> Hi Alexander,
>>>
>>> On Fri, Oct 12, 2012 at 4:34 AM, Alexander Duyck
>>> <alexander.h.duyck@intel.com> wrote:
>>>> This change replaces all references to the virtual address for io_tlb_end
>>>> with references to the physical address io_tlb_end.  The main advantage of
>>>> replacing the virtual address with a physical address is that we can avoid
>>>> having to do multiple translations from the virtual address to the physical
>>>> one needed for testing an existing DMA address.
>>>>
>>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
>>>> ---
>>>>
>>>>  lib/swiotlb.c |   24 +++++++++++++-----------
>>>>  1 files changed, 13 insertions(+), 11 deletions(-)
>>>>
>>>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
>>>> index f114bf6..19aac9f 100644
>>>> --- a/lib/swiotlb.c
>>>> +++ b/lib/swiotlb.c
>>>> @@ -57,7 +57,8 @@ int swiotlb_force;
>>>>   * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
>>>>   * API.
>>>>   */
>>>> -static char *io_tlb_start, *io_tlb_end;
>>>> +static char *io_tlb_start;
>>>> +phys_addr_t io_tlb_end;
>>> If add io_tlb_start_phy and io_tlb_end_phy, could we get same results
>>> with less hunks?
>>>
>>> Hillf
>> What do you mean by less hunks?  Are you referring to the memory space? 
> As in less patch movements.
>> If so, then the patches I am submitting do not impact how much space is
>> used for the bounce buffer.  The only real result of these patches is
>> that the total code path is significantly reduced since we don't have to
>> perform any virtual to physical translations in the hot-path.
> No. He is referring that you can keep io_tlb_end still here. Just
> do the computation of the physical address in the init path (of the end).
> Then you don't need to do the shifting in the 'is-this-swiotlb-buffer'
> and can just do a simple:
> 	if (dma_addr >= io_tlb_start && dma_addr <= io_tlb_end)
>

That is how the code ends up.  The v2 and v3 version of these patches
leave the end value there.  As this patch says I am just changing the
end to be physical instead of virtual.  I reviewed the code and realized
that I wasn't saving anything by removing it since the overall code was
larger as a result so I just converted it to a physical address.  There
are no users of io_tlb_end that are accessing it as a virtual value so
all I did is just change it to a physical one and drop the virt_to_phys
calls that were made on it.  If I am not mistaken by the second patch
the is_swiotlb_buffer call is literally what you have described above. 
Here is the snippet from the 2nd patch:

static int is_swiotlb_buffer(phys_addr_t paddr)
 {
-	return paddr >= virt_to_phys(io_tlb_start) && paddr < io_tlb_end;
+	return paddr >= io_tlb_start && paddr < io_tlb_end;
 }


As far as the number of patches I decided to do this incrementally
instead of trying to do it all at once.  That way it is clearer to the
reviewer what I am doing in each step and it can be more easily bisected
in case I messed up somewhere.  If you want fewer patches I can do that
but I don't see the point in combining patches since they are all just
going to result in the same total change anyway.

Thanks,

Alex

Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

[Konrad Rzeszutek Wilk]

On Thu, Oct 18, 2012 at 08:53:33AM -0700, Alexander Duyck wrote:
> On 10/18/2012 05:41 AM, Konrad Rzeszutek Wilk wrote:
> > On Mon, Oct 15, 2012 at 08:43:28AM -0700, Alexander Duyck wrote:
> >> On 10/13/2012 05:52 AM, Hillf Danton wrote:
> >>> Hi Alexander,
> >>>
> >>> On Fri, Oct 12, 2012 at 4:34 AM, Alexander Duyck
> >>> <alexander.h.duyck@intel.com> wrote:
> >>>> This change replaces all references to the virtual address for io_tlb_end
> >>>> with references to the physical address io_tlb_end.  The main advantage of
> >>>> replacing the virtual address with a physical address is that we can avoid
> >>>> having to do multiple translations from the virtual address to the physical
> >>>> one needed for testing an existing DMA address.
> >>>>
> >>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> >>>> ---
> >>>>
> >>>>  lib/swiotlb.c |   24 +++++++++++++-----------
> >>>>  1 files changed, 13 insertions(+), 11 deletions(-)
> >>>>
> >>>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> >>>> index f114bf6..19aac9f 100644
> >>>> --- a/lib/swiotlb.c
> >>>> +++ b/lib/swiotlb.c
> >>>> @@ -57,7 +57,8 @@ int swiotlb_force;
> >>>>   * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
> >>>>   * API.
> >>>>   */
> >>>> -static char *io_tlb_start, *io_tlb_end;
> >>>> +static char *io_tlb_start;
> >>>> +phys_addr_t io_tlb_end;
> >>> If add io_tlb_start_phy and io_tlb_end_phy, could we get same results
> >>> with less hunks?
> >>>
> >>> Hillf
> >> What do you mean by less hunks?  Are you referring to the memory space? 
> > As in less patch movements.
> >> If so, then the patches I am submitting do not impact how much space is
> >> used for the bounce buffer.  The only real result of these patches is
> >> that the total code path is significantly reduced since we don't have to
> >> perform any virtual to physical translations in the hot-path.
> > No. He is referring that you can keep io_tlb_end still here. Just
> > do the computation of the physical address in the init path (of the end).
> > Then you don't need to do the shifting in the 'is-this-swiotlb-buffer'
> > and can just do a simple:
> > 	if (dma_addr >= io_tlb_start && dma_addr <= io_tlb_end)
> >
> 
> That is how the code ends up.  The v2 and v3 version of these patches
> leave the end value there.  As this patch says I am just changing the

Great!
> end to be physical instead of virtual.  I reviewed the code and realized
> that I wasn't saving anything by removing it since the overall code was
> larger as a result so I just converted it to a physical address.  There
> are no users of io_tlb_end that are accessing it as a virtual value so
> all I did is just change it to a physical one and drop the virt_to_phys
> calls that were made on it.  If I am not mistaken by the second patch
> the is_swiotlb_buffer call is literally what you have described above. 
> Here is the snippet from the 2nd patch:
> 
> static int is_swiotlb_buffer(phys_addr_t paddr)
>  {
> -	return paddr >= virt_to_phys(io_tlb_start) && paddr < io_tlb_end;
> +	return paddr >= io_tlb_start && paddr < io_tlb_end;
>  }
> 
> 
> As far as the number of patches I decided to do this incrementally
> instead of trying to do it all at once.  That way it is clearer to the
> reviewer what I am doing in each step and it can be more easily bisected
> in case I messed up somewhere.  If you want fewer patches I can do that
> but I don't see the point in combining patches since they are all just
> going to result in the same total change anyway.

No that is OK. BTW, I did a testing of your V2 patches with Xen-SWIOTLB
and they worked. But it was on non-debug env. The debug one does such
evil things as make the initial domain memory start at the end physical
memory and put the underlaying MFNs (machine frame numbers, the real
physical frames) in reverse order. So for example pfn 100, ends up being
mfn 0xf00d, and pfn 101 ends up being oxf00c.

Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

[Alexander Duyck]

On 10/19/2012 07:18 AM, Konrad Rzeszutek Wilk wrote:
> On Thu, Oct 18, 2012 at 08:53:33AM -0700, Alexander Duyck wrote:
>> end to be physical instead of virtual.  I reviewed the code and realized
>> that I wasn't saving anything by removing it since the overall code was
>> larger as a result so I just converted it to a physical address.  There
>> are no users of io_tlb_end that are accessing it as a virtual value so
>> all I did is just change it to a physical one and drop the virt_to_phys
>> calls that were made on it.  If I am not mistaken by the second patch
>> the is_swiotlb_buffer call is literally what you have described above. 
>> Here is the snippet from the 2nd patch:
>>
>> static int is_swiotlb_buffer(phys_addr_t paddr)
>>  {
>> -	return paddr >= virt_to_phys(io_tlb_start) && paddr < io_tlb_end;
>> +	return paddr >= io_tlb_start && paddr < io_tlb_end;
>>  }
>>
>>
>> As far as the number of patches I decided to do this incrementally
>> instead of trying to do it all at once.  That way it is clearer to the
>> reviewer what I am doing in each step and it can be more easily bisected
>> in case I messed up somewhere.  If you want fewer patches I can do that
>> but I don't see the point in combining patches since they are all just
>> going to result in the same total change anyway.
> No that is OK. BTW, I did a testing of your V2 patches with Xen-SWIOTLB
> and they worked. But it was on non-debug env. The debug one does such
> evil things as make the initial domain memory start at the end physical
> memory and put the underlaying MFNs (machine frame numbers, the real
> physical frames) in reverse order. So for example pfn 100, ends up being
> mfn 0xf00d, and pfn 101 ends up being oxf00c.

Glad to hear they are working under Xen.  As I said I am pretty sure if
it was working before it should still be working after these changes
since the only difference is that instead of working with virtual
addresses and having to call virt_to_phys to get the pseudo-physical
addresses we are just working with the pseudo-physical addresses directly.

Thanks,

Alex