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Subject[PATCH] swiotlb: Add support to disable swiotlb overflow buffer with deprecation warning
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Date
Add support for disabling swiotlb overflow buffer using zero size swiotlb
overflow buffer to help test disable overflow scenarios to find drivers that
don't check dma mapping errors. Add kernel error message to track overflow
buffer triggers to understand how often overflow buffer gets used. Add
deprecation notice warning message and deprecation schedule documentation, as
a first step towards removing overflow support, to be consistent with other
iommu implementations and return DMA_ERROR_CODE. Once drivers are fixed
overflow support can be removed.

Tested on x86-64 and compile tested on IA64.

Signed-off-by: Shuah Khan <shuah.khan@hp.com>
---
Documentation/feature-removal-schedule.txt | 15 ++++++
lib/swiotlb.c | 73 ++++++++++++++++++++--------
2 files changed, 69 insertions(+), 19 deletions(-)
diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index a52924e..b5938ca 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -646,3 +646,18 @@ Who: Russell King <linux@arm.linux.org.uk>,
Santosh Shilimkar <santosh.shilimkar@ti.com>

----------------------------
+
+What: SWIOTLB overflow buffer support.
+When: 3.8
+Why: Remove SWIOTLB overflow buffer support and return DMA_ERROR_CODE
+ (a value of zero) to make it consistent with iommu implementation
+ on Intel, AMD, and swiotlb-xen. In 3.7, add logging to track swiotlb
+ buffer overflow triggers to understand how often overflow buffer
+ gets used. The next step is to fix drivers that don't call
+ dma_mapping_error to check for errors returned by the mapping
+ interfaces. Once drivers are fixed overflow support can be removed.
+ If you see any problems related to disabling SWIOTLB overflow buffer,
+ please report to us!
+ E-mail us at: linux-kernel@vger.kernel.org
+Who: Shuah Khan <shuah.khan@hp.com> <shuahkhan@gmail.com>
+
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 45bc1f8..658f35a 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -92,6 +92,24 @@ static DEFINE_SPINLOCK(io_tlb_lock);

static int late_alloc;

+static void swiotlb_print_overflow_deprecation_notice(void)
+{
+ if (io_tlb_overflow) {
+ pr_warn("SWIOTLB overflow buffer will be deprecated.\n"
+ " If you have a driver that depends on this feature\n"
+ " please Email us at: linux-kernel@vger.kernel.org,\n"
+ " Shuah Khan (shuahkhan@gmail.com), and\n"
+ " Konrad Wilk (konrad.wilk@oracle.com)\n");
+ } else {
+ pr_warn("SWIOTLB overflow buffer is disabled and will be\n"
+ " deprecated. Please report problems related to\n"
+ " disabling overflow buffer to\n"
+ " linux-kernel@vger.kernel.org,\n"
+ " Shuah Khan (shuahkhan@gmail.com), and\n"
+ " Konrad Wilk (konrad.wilk@oracle.com)\n");
+ }
+}
+
static int __init
setup_io_tlb_npages(char *str)
{
@@ -108,7 +126,6 @@ setup_io_tlb_npages(char *str)
return 1;
}
__setup("swiotlb=", setup_io_tlb_npages);
-/* make io_tlb_overflow tunable too? */

unsigned long swiotlb_nr_tbl(void)
{
@@ -156,12 +173,18 @@ 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 (io_tlb_overflow) {
+ /*
+ * 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");
+ }
+
+ swiotlb_print_overflow_deprecation_notice();
+
if (verbose)
swiotlb_print_info();
}
@@ -264,14 +287,17 @@ swiotlb_late_init_with_default_size(size_t default_size)

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;
+ if (io_tlb_overflow) {
+ /*
+ * 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_overflow_deprecation_notice();
swiotlb_print_info();

late_alloc = 1;
@@ -297,12 +323,13 @@ cleanup1:

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,
- get_order(io_tlb_overflow));
+ if (io_tlb_overflow_buffer)
+ free_pages((unsigned long)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)));
free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
@@ -310,8 +337,9 @@ void __init swiotlb_free(void)
free_pages((unsigned long)io_tlb_start,
get_order(io_tlb_nslabs << IO_TLB_SHIFT));
} else {
- free_bootmem_late(__pa(io_tlb_overflow_buffer),
- PAGE_ALIGN(io_tlb_overflow));
+ if (io_tlb_overflow_buffer)
+ free_bootmem_late(__pa(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)));
free_bootmem_late(__pa(io_tlb_list),
@@ -681,7 +709,10 @@ 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);
+ if (!io_tlb_overflow)
+ return DMA_ERROR_CODE;
map = io_tlb_overflow_buffer;
+ dev_err(dev, "SWIOTLB is full. Mapping overflow buffer.\n");
}

dev_addr = swiotlb_virt_to_bus(dev, map);
@@ -691,6 +722,8 @@ 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);
+ if (!io_tlb_overflow)
+ return DMA_ERROR_CODE;
dev_addr = swiotlb_virt_to_bus(dev, io_tlb_overflow_buffer);
}

@@ -910,6 +943,8 @@ EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
int
swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
{
+ if (!io_tlb_overflow)
+ return DMA_ERROR_CODE;
return (dma_addr == swiotlb_virt_to_bus(hwdev, io_tlb_overflow_buffer));
}
EXPORT_SYMBOL(swiotlb_dma_mapping_error);
--
1.7.9.5




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