swiotlb: Correct kernel command line handler

This patch corrects kernel command line handler when io_tlb_nslabs is set to 0.

A current implementation allocates default size memory (64MB) when 0 is given to io_tlb_nslabs ("swiotlb=0") by kernel command line. In other words, memory is allocated unintentionally.

Signed-off-by Jungseok Lee <[email protected]>

Signed-off-by Sungjinn Chung <[email protected]>

---
 lib/swiotlb.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

lib/swiotlb.c +6 -2

index b604b83..9fe9f71 100644
@@ -55,6 +55,8 @@
 
 int swiotlb_force;
 
+static int swiotlb_no_use;
+
 /*
  * Used to do a quick range check in swiotlb_tbl_unmap_single and
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this

@@ -102,6 +104,8 @@ setup_io_tlb_npages(char *str)
 		io_tlb_nslabs = simple_strtoul(str, &str, 0);
 		/* avoid tail segment of size < IO_TLB_SEGSIZE */
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
+		if (!io_tlb_nslabs)
+			swiotlb_no_use = 1;
 	}
 	if (*str == ',')
 		++str;

@@ -212,7 +216,7 @@ swiotlb_init(int verbose)
 	unsigned char *vstart;
 	unsigned long bytes;
 
-	if (!io_tlb_nslabs) {
+	if (!swiotlb_no_use && !io_tlb_nslabs) {
 		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
 	}

@@ -244,7 +248,7 @@ swiotlb_late_init_with_default_size(size_t default_size)
 	unsigned int order;
 	int rc = 0;
 
-	if (!io_tlb_nslabs) {
+	if (!swiotlb_no_use && !io_tlb_nslabs) {
 		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
 	}

Signature · 1 line

1.7.10.4

Quoted 6 lines · Jungseok Lee

This patch corrects kernel command line handler when io_tlb_nslabs is set to 0.

A current implementation allocates default size memory (64MB) when 0 is given to io_tlb_nslabs ("swiotlb=0") by kernel command line. In other words, memory is allocated unintentionally.

What are the other IOMMUs that end up taking over the DMA ops?

Or do you end up with no DMA ops?

Quoted 48 lines

Signed-off-by Jungseok Lee <[email protected]>

Signed-off-by Sungjinn Chung <[email protected]>

---
 lib/swiotlb.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

lib/swiotlb.c index b604b83..9fe9f71 renamed from lib/swiotlb.c +0 -0

100644

lib/swiotlb.c +2 -0

@@ -55,6 +55,8 @@
 
 int swiotlb_force;
 
+static int swiotlb_no_use;
+
 /*
  * Used to do a quick range check in swiotlb_tbl_unmap_single and
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact

allocated by this @@ -102,6 +104,8 @@ setup_io_tlb_npages(char *str)

lib/swiotlb.c +4 -3

 		io_tlb_nslabs = simple_strtoul(str, &str, 0);
 		/* avoid tail segment of size < IO_TLB_SEGSIZE */
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
+		if (!io_tlb_nslabs)
+			swiotlb_no_use = 1;
 	}
 	if (*str == ',')
 		++str;

@@ -212,7 +216,7 @@ swiotlb_init(int verbose)
 	unsigned char *vstart;
 	unsigned long bytes;
 
-	if (!io_tlb_nslabs) {
+	if (!swiotlb_no_use && !io_tlb_nslabs) {
 		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
 	}

@@ -244,7 +248,7 @@ swiotlb_late_init_with_default_size(size_t default_size)
 	unsigned int order;
 	int rc = 0;
 
-	if (!io_tlb_nslabs) {
+	if (!swiotlb_no_use && !io_tlb_nslabs) {
 		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
 	}
--

Quoted 3 lines

1.7.10.4

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Quoted 9 lines · Konrad Rzeszutek Wilk

Quoted 6 lines · Jungseok Lee

This patch corrects kernel command line handler when io_tlb_nslabs is set to 0.

A current implementation allocates default size memory (64MB) when 0 is given to io_tlb_nslabs ("swiotlb=0") by kernel command line. In other words, memory is allocated unintentionally.

What are the other IOMMUs that end up taking over the DMA ops?

I think that no other IOMMUs take over it on ARM64 system, except Xen.

Quoted 1 line

Or do you end up with no DMA ops?

I focus on ARM64 system which uses swiotlb as default DMA ops.

If some ARM64 platforms would like to use memory only from __get_free_pages in swiotlb_alloc_coherent function, an interface would be needed to configure reserved memory size.

Thus, I add it to kernel command line handler.

Best Regards
Jungseok Lee

Quoted 54 lines

Quoted 48 lines

Signed-off-by Jungseok Lee <[email protected]>

Signed-off-by Sungjinn Chung <[email protected]>

---
 lib/swiotlb.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

lib/swiotlb.c index b604b83..9fe9f71 renamed from lib/swiotlb.c +0 -0

100644

lib/swiotlb.c +2 -0

@@ -55,6 +55,8 @@
 
 int swiotlb_force;
 
+static int swiotlb_no_use;
+
 /*
  * Used to do a quick range check in swiotlb_tbl_unmap_single and
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact

allocated by this @@ -102,6 +104,8 @@ setup_io_tlb_npages(char *str)

lib/swiotlb.c +4 -3

 		io_tlb_nslabs = simple_strtoul(str, &str, 0);
 		/* avoid tail segment of size < IO_TLB_SEGSIZE */
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
+		if (!io_tlb_nslabs)
+			swiotlb_no_use = 1;
 	}
 	if (*str == ',')
 		++str;

@@ -212,7 +216,7 @@ swiotlb_init(int verbose)
 	unsigned char *vstart;
 	unsigned long bytes;
 
-	if (!io_tlb_nslabs) {
+	if (!swiotlb_no_use && !io_tlb_nslabs) {
 		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
 	}

@@ -244,7 +248,7 @@ swiotlb_late_init_with_default_size(size_t default_size)
 	unsigned int order;
 	int rc = 0;
 
-	if (!io_tlb_nslabs) {
+	if (!swiotlb_no_use && !io_tlb_nslabs) {
 		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
 	}
--

Quoted 3 lines

1.7.10.4

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