* [PATCH v2] dma-debug: Check scatterlist segments
@ 2018-05-14 13:06 Robin Murphy
2018-05-17 19:50 ` kbuild test robot
0 siblings, 1 reply; 2+ messages in thread
From: Robin Murphy @ 2018-05-14 13:06 UTC (permalink / raw)
To: hch-jcswGhMUV9g, m.szyprowski-Sze3O3UU22JBDgjK7y7TUQ
Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA,
linux-kernel-u79uwXL29TY76Z2rM5mHXA
Drivers/subsystems creating scatterlists for DMA should be taking care
to respect the scatter-gather limitations of the appropriate device, as
described by dma_parms. A DMA API implementation cannot feasibly split
a scatterlist into *more* entries than originally passed, so it is not
well defined what they should do when given a segment larger than the
limit they are also required to respect.
Conversely, devices which are less limited than the rather conservative
defaults, or indeed have no limitations at all (e.g. GPUs with their own
internal MMU), should be encouraged to set appropriate dma_parms, as
they may get more efficient DMA mapping performance out of it.
Signed-off-by: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
---
v2: Wrap it a separate config option - default y/n is open for debate
lib/Kconfig.debug | 17 +++++++++++++++++
lib/dma-debug.c | 28 ++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c40c7b734cd1..5fc326d84ae7 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1651,6 +1651,23 @@ config DMA_API_DEBUG
If unsure, say N.
+config DMA_API_DEBUG_SG
+ bool "Debug DMA scatter-gather usage"
+ default y
+ depends on DMA_API_DEBUG
+ help
+ Perform extra checking that callers of dma_map_sg() have respected the
+ appropriate segment length/boundary limits for the given device when
+ preparing DMA scatterlists.
+
+ This is particularly likely to have been overlooked in cases where the
+ dma_map_sg() API is used for general bulk mapping of pages rather than
+ preparing literal scatter-gather descriptors, where there is a risk of
+ unexpected behaviour from DMA API implementations if the scatterlist is
+ technically out-of-spec.
+
+ If unsure, say N.
+
menuconfig RUNTIME_TESTING_MENU
bool "Runtime Testing"
def_bool y
diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 7f5cdc1e6b29..c522f3ef80a6 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1293,6 +1293,32 @@ static void check_sync(struct device *dev,
put_hash_bucket(bucket, &flags);
}
+static void check_sg_segment(struct device *dev, struct scatterlist *sg)
+{
+#ifdef CONFIG_DMA_API_DEBUG_SG
+ unsigned int max_seg = dma_get_max_seg_size(dev);
+ dma_addr_t start, end, boundary = dma_get_seg_boundary(dev);
+
+ /*
+ * Either the driver forgot to set dma_parms appropriately, or
+ * whoever generated the list forgot to check them.
+ */
+ if (sg->length > max_seg)
+ err_printk(dev, NULL, "DMA-API: mapping sg segment longer than device claims to support [len=%u] [max=%u]\n",
+ sg->length, max_seg);
+ /*
+ * In some cases this could potentially be the DMA API
+ * implementation's fault, but it would usually imply that
+ * the scatterlist was built inappropriately to begin with.
+ */
+ start = sg_dma_address(sg);
+ end = start + sg_dma_len(sg) - 1;
+ if ((start ^ end) & ~boundary)
+ err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
+ start, end, boundary);
+#endif
+}
+
void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
size_t size, int direction, dma_addr_t dma_addr,
bool map_single)
@@ -1423,6 +1449,8 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
check_for_illegal_area(dev, sg_virt(s), sg_dma_len(s));
}
+ check_sg_segment(dev, s);
+
add_dma_entry(entry);
}
}
--
2.17.0.dirty
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] dma-debug: Check scatterlist segments
2018-05-14 13:06 [PATCH v2] dma-debug: Check scatterlist segments Robin Murphy
@ 2018-05-17 19:50 ` kbuild test robot
0 siblings, 0 replies; 2+ messages in thread
From: kbuild test robot @ 2018-05-17 19:50 UTC (permalink / raw)
To: Robin Murphy; +Cc: kbuild-all, hch, m.szyprowski, iommu, linux-kernel
[-- Attachment #1: Type: text/plain, Size: 7136 bytes --]
Hi Robin,
I love your patch! Perhaps something to improve:
[auto build test WARNING on linus/master]
[also build test WARNING on v4.17-rc5 next-20180517]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Robin-Murphy/dma-debug-Check-scatterlist-segments/20180514-220916
config: sh-allyesconfig (attached as .config)
compiler: sh4-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=sh
All warnings (new ones prefixed by >>):
In file included from arch/sh/include/asm/bug.h:112:0,
from include/linux/bug.h:5,
from include/linux/thread_info.h:12,
from include/asm-generic/current.h:5,
from ./arch/sh/include/generated/asm/current.h:1,
from include/linux/sched.h:12,
from include/linux/sched/task_stack.h:9,
from lib/dma-debug.c:20:
lib/dma-debug.c: In function 'check_sg_segment':
>> lib/dma-debug.c:232:12: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 4 has type 'dma_addr_t {aka unsigned int}' [-Wformat=]
WARN(1, "%s %s: " format, \
^
include/asm-generic/bug.h:98:50: note: in definition of macro '__WARN_printf'
#define __WARN_printf(arg...) do { __warn_printk(arg); __WARN(); } while (0)
^~~
>> lib/dma-debug.c:232:4: note: in expansion of macro 'WARN'
WARN(1, "%s %s: " format, \
^~~~
>> lib/dma-debug.c:1317:3: note: in expansion of macro 'err_printk'
err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
^~~~~~~~~~
lib/dma-debug.c:1317:85: note: format string is defined here
err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
~~~~~~^
%016x
In file included from arch/sh/include/asm/bug.h:112:0,
from include/linux/bug.h:5,
from include/linux/thread_info.h:12,
from include/asm-generic/current.h:5,
from ./arch/sh/include/generated/asm/current.h:1,
from include/linux/sched.h:12,
from include/linux/sched/task_stack.h:9,
from lib/dma-debug.c:20:
lib/dma-debug.c:232:12: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 5 has type 'dma_addr_t {aka unsigned int}' [-Wformat=]
WARN(1, "%s %s: " format, \
^
include/asm-generic/bug.h:98:50: note: in definition of macro '__WARN_printf'
#define __WARN_printf(arg...) do { __warn_printk(arg); __WARN(); } while (0)
^~~
>> lib/dma-debug.c:232:4: note: in expansion of macro 'WARN'
WARN(1, "%s %s: " format, \
^~~~
>> lib/dma-debug.c:1317:3: note: in expansion of macro 'err_printk'
err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
^~~~~~~~~~
lib/dma-debug.c:1317:101: note: format string is defined here
err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
~~~~~~^
%016x
In file included from arch/sh/include/asm/bug.h:112:0,
from include/linux/bug.h:5,
from include/linux/thread_info.h:12,
from include/asm-generic/current.h:5,
from ./arch/sh/include/generated/asm/current.h:1,
from include/linux/sched.h:12,
from include/linux/sched/task_stack.h:9,
from lib/dma-debug.c:20:
lib/dma-debug.c:232:12: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 6 has type 'dma_addr_t {aka unsigned int}' [-Wformat=]
WARN(1, "%s %s: " format, \
^
include/asm-generic/bug.h:98:50: note: in definition of macro '__WARN_printf'
#define __WARN_printf(arg...) do { __warn_printk(arg); __WARN(); } while (0)
^~~
>> lib/dma-debug.c:232:4: note: in expansion of macro 'WARN'
WARN(1, "%s %s: " format, \
^~~~
>> lib/dma-debug.c:1317:3: note: in expansion of macro 'err_printk'
err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
^~~~~~~~~~
lib/dma-debug.c:1317:122: note: format string is defined here
err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
~~~~~~^
%016x
vim +232 lib/dma-debug.c
2e507d84 Joerg Roedel 2009-05-22 227
6c132d1b David Woodhouse 2009-01-19 228 #define err_printk(dev, entry, format, arg...) do { \
2d62ece1 Joerg Roedel 2009-01-09 229 error_count += 1; \
2e507d84 Joerg Roedel 2009-05-22 230 if (driver_filter(dev) && \
2e507d84 Joerg Roedel 2009-05-22 231 (show_all_errors || show_num_errors > 0)) { \
2d62ece1 Joerg Roedel 2009-01-09 @232 WARN(1, "%s %s: " format, \
ec9c96ef Kyle McMartin 2009-08-19 233 dev ? dev_driver_string(dev) : "NULL", \
ec9c96ef Kyle McMartin 2009-08-19 234 dev ? dev_name(dev) : "NULL", ## arg); \
6c132d1b David Woodhouse 2009-01-19 235 dump_entry_trace(entry); \
2d62ece1 Joerg Roedel 2009-01-09 236 } \
2d62ece1 Joerg Roedel 2009-01-09 237 if (!show_all_errors && show_num_errors > 0) \
2d62ece1 Joerg Roedel 2009-01-09 238 show_num_errors -= 1; \
2d62ece1 Joerg Roedel 2009-01-09 239 } while (0);
2d62ece1 Joerg Roedel 2009-01-09 240
:::::: The code at line 232 was first introduced by commit
:::::: 2d62ece14fe04168a7d16688ddd2d17ac472268c dma-debug: add core checking functions
:::::: TO: Joerg Roedel <joerg.roedel@amd.com>
:::::: CC: Joerg Roedel <joerg.roedel@amd.com>
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
[-- Attachment #2: .config.gz --]
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