dma-debug: update DMA debug API to better handle multiple mappings of a buffer

There were reports of the igb driver unmapping buffers without calling
dma_mapping_error.  On closer inspection issues were found in the DMA
debug API and how it handled multiple mappings of the same buffer.

The issue I found is the fact that the debug_dma_mapping_error would
only set the map_err_type to MAP_ERR_CHECKED in the case that the was
only one match for device and device address.  However in the case of
non-IOMMU, multiple addresses existed and as a result it was not setting
this field once a second mapping was instantiated.  I have resolved this
by changing the search so that it instead will now set MAP_ERR_CHECKED
on the first buffer that matches the device and DMA address that is
currently in the state MAP_ERR_NOT_CHECKED.

A secondary side effect of this patch is that in the case of multiple
buffers using the same address only the last mapping will have a valid
map_err_type.  The previous mappings will all end up with map_err_type
set to MAP_ERR_CHECKED because of the dma_mapping_error call in
debug_dma_map_page.  However this behavior may be preferable as it means
you will likely only see one real error per multi-mapped buffer, versus
the current behavior of multiple false errors mer multi-mapped buffer.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Reviewed-by: Shuah Khan <shuah.khan@hp.com>
Tested-by: Shuah Khan <shuah.khan@hp.com>
Cc: Jakub Kicinski <kubakici@wp.pl>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 5 deletions

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index d3e06a5e981e..d87a17a819d0 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1085,13 +1085,27 @@ void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
         ref.dev = dev;
         ref.dev_addr = dma_addr;
         bucket = get_hash_bucket(&ref, &flags);
-        entry = bucket_find_exact(bucket, &ref);
 
-        if (!entry)
-                goto out;
+        list_for_each_entry(entry, &bucket->list, list) {
+                if (!exact_match(&ref, entry))
+                        continue;
+
+                /*
+                 * The same physical address can be mapped multiple
+                 * times. Without a hardware IOMMU this results in the
+                 * same device addresses being put into the dma-debug
+                 * hash multiple times too. This can result in false
+                 * positives being reported. Therefore we implement a
+                 * best-fit algorithm here which updates the first entry
+                 * from the hash which fits the reference value and is
+                 * not currently listed as being checked.
+                 */
+                if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
+                        entry->map_err_type = MAP_ERR_CHECKED;
+                        break;
+                }
+        }
 
-        entry->map_err_type = MAP_ERR_CHECKED;
-out:
         put_hash_bucket(bucket, &flags);
 }
 EXPORT_SYMBOL(debug_dma_mapping_error);