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Date: Tue, 14 Jan 2014 14:04:31 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: dmaengine@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
netdev@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
linux-kernel@...r.kernel.org,
James Bottomley <JBottomley@...allels.com>,
Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH v3 4/4] dma debug: introduce debug_dma_assert_idle()
On Mon, 2014-01-13 at 17:14 -0800, Andrew Morton wrote:
> On Mon, 13 Jan 2014 16:48:47 -0800 Dan Williams <dan.j.williams@...el.com> wrote:
>
> > Record actively mapped pages and provide an api for asserting a given
> > page is dma inactive before execution proceeds. Placing
> > debug_dma_assert_idle() in cow_user_page() flagged the violation of the
> > dma-api in the NET_DMA implementation (see commit 77873803363c "net_dma:
> > mark broken").
>
> Some discussion of the overlap counter thing would be useful.
>
[..]
> OK, I think I see what's happening. The tags thing acts as a crude
> counter and if the map/unmap count ends up imbalanced, we deliberately
> leak an entry in the radix-tree so it can later be reported via undescribed
> means. Thoughts:
>
> - RADIX_TREE_MAX_TAGS=3 so the code could count to 7, with a bit of
> futzing around.
>
> - from a style/readability point of view it is unexpected that
> __active_pfn_dec_overlap() actually removes radix-tree items. It
> would be better to do:
>
> spin_lock_irqsave(&radix_lock, flags);
> if (__active_pfn_dec_overlap(entry) == something) {
> /*
> * Nice comment goes here
> */
> radix_tree_delete(...);
> }
> spin_unlock_irqrestore(&radix_lock, flags);
>
>
Ok, here is v4, let me know if you prefer a new mail or if the
'scissors' are sufficient:
>8-----------------
From: Dan Williams <dan.j.williams@...el.com>
Date: Tue, 17 Dec 2013 12:31:34 -0800
Subject: [PATCH v4] dma debug: introduce debug_dma_assert_idle()
Record actively mapped pages and provide an api for asserting a given
page is dma inactive before execution proceeds. Placing
debug_dma_assert_idle() in cow_user_page() flagged the violation of the
dma-api in the NET_DMA implementation (see commit 77873803363c "net_dma:
mark broken").
The implementation includes the capability to count, in a limited way,
repeat mappings of the same page that occur without an intervening
unmap. This 'overlap' counter is limited to the few bits of tag space
in a radix tree. This mechanism is added to mitigate false negative
cases where, for example, a page is dma mapped twice and
debug_dma_assert_idle() is called after the page is un-mapped once.
Cc: Joerg Roedel <joro@...tes.org>
Cc: Vinod Koul <vinod.koul@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Russell King <rmk+kernel@....linux.org.uk>
Cc: James Bottomley <JBottomley@...allels.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
include/linux/dma-debug.h | 6 ++
lib/Kconfig.debug | 12 +++-
lib/dma-debug.c | 193 ++++++++++++++++++++++++++++++++++++++++++---
mm/memory.c | 3 +
4 files changed, 199 insertions(+), 15 deletions(-)
diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h
index fc0e34ce038f..fe8cb610deac 100644
--- a/include/linux/dma-debug.h
+++ b/include/linux/dma-debug.h
@@ -85,6 +85,8 @@ extern void debug_dma_sync_sg_for_device(struct device *dev,
extern void debug_dma_dump_mappings(struct device *dev);
+extern void debug_dma_assert_idle(struct page *page);
+
#else /* CONFIG_DMA_API_DEBUG */
static inline void dma_debug_add_bus(struct bus_type *bus)
@@ -183,6 +185,10 @@ static inline void debug_dma_dump_mappings(struct device *dev)
{
}
+static inline void debug_dma_assert_idle(struct page *page)
+{
+}
+
#endif /* CONFIG_DMA_API_DEBUG */
#endif /* __DMA_DEBUG_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index db25707aa41b..20073e7156e4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1575,8 +1575,16 @@ config DMA_API_DEBUG
With this option you will be able to detect common bugs in device
drivers like double-freeing of DMA mappings or freeing mappings that
were never allocated.
- This option causes a performance degredation. Use only if you want
- to debug device drivers. If unsure, say N.
+
+ This also attempts to catch cases where a page owned by DMA is
+ accessed by the cpu in a way that could cause data corruption. For
+ example, this enables cow_user_page() to check that the source page is
+ not undergoing DMA.
+
+ This option causes a performance degradation. Use only if you want to
+ debug device drivers and dma interactions.
+
+ If unsure, say N.
source "samples/Kconfig"
diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index d87a17a819d0..c38083871f11 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -53,11 +53,26 @@ enum map_err_types {
#define DMA_DEBUG_STACKTRACE_ENTRIES 5
+/**
+ * struct dma_debug_entry - track a dma_map* or dma_alloc_coherent mapping
+ * @list: node on pre-allocated free_entries list
+ * @dev: 'dev' argument to dma_map_{page|single|sg} or dma_alloc_coherent
+ * @type: single, page, sg, coherent
+ * @pfn: page frame of the start address
+ * @offset: offset of mapping relative to pfn
+ * @size: length of the mapping
+ * @direction: enum dma_data_direction
+ * @sg_call_ents: 'nents' from dma_map_sg
+ * @sg_mapped_ents: 'mapped_ents' from dma_map_sg
+ * @map_err_type: track whether dma_mapping_error() was checked
+ * @stacktrace: support backtraces when a violation is detected
+ */
struct dma_debug_entry {
struct list_head list;
struct device *dev;
int type;
- phys_addr_t paddr;
+ unsigned long pfn;
+ size_t offset;
u64 dev_addr;
u64 size;
int direction;
@@ -372,6 +387,11 @@ static void hash_bucket_del(struct dma_debug_entry *entry)
list_del(&entry->list);
}
+static unsigned long long phys_addr(struct dma_debug_entry *entry)
+{
+ return page_to_phys(pfn_to_page(entry->pfn)) + entry->offset;
+}
+
/*
* Dump mapping entries for debugging purposes
*/
@@ -389,9 +409,9 @@ void debug_dma_dump_mappings(struct device *dev)
list_for_each_entry(entry, &bucket->list, list) {
if (!dev || dev == entry->dev) {
dev_info(entry->dev,
- "%s idx %d P=%Lx D=%Lx L=%Lx %s %s\n",
+ "%s idx %d P=%Lx N=%lx D=%Lx L=%Lx %s %s\n",
type2name[entry->type], idx,
- (unsigned long long)entry->paddr,
+ phys_addr(entry), entry->pfn,
entry->dev_addr, entry->size,
dir2name[entry->direction],
maperr2str[entry->map_err_type]);
@@ -404,6 +424,133 @@ void debug_dma_dump_mappings(struct device *dev)
EXPORT_SYMBOL(debug_dma_dump_mappings);
/*
+ * For each page mapped (initial page in the case of
+ * dma_alloc_coherent/dma_map_{single|page}, or each page in a
+ * scatterlist) insert into this tree using the pfn as the key. At
+ * dma_unmap_{single|sg|page} or dma_free_coherent delete the entry. If
+ * the pfn already exists at insertion time add a tag as a reference
+ * count for the overlapping mappings. For now, the overlap tracking
+ * just ensures that 'unmaps' balance 'maps' before marking the pfn
+ * idle, but we should also be flagging overlaps as an API violation.
+ *
+ * Memory usage is mostly constrained by the maximum number of available
+ * dma-debug entries in that we need a free dma_debug_entry before
+ * inserting into the tree. In the case of dma_map_{single|page} and
+ * dma_alloc_coherent there is only one dma_debug_entry and one pfn to
+ * track per event. dma_map_sg(), on the other hand,
+ * consumes a single dma_debug_entry, but inserts 'nents' entries into
+ * the tree.
+ *
+ * At any time debug_dma_assert_idle() can be called to trigger a
+ * warning if the given page is in the active set.
+ */
+static RADIX_TREE(dma_active_pfn, GFP_NOWAIT);
+static DEFINE_SPINLOCK(radix_lock);
+#define ACTIVE_PFN_MAX_OVERLAP ((1 << RADIX_TREE_MAX_TAGS) - 1)
+
+static int active_pfn_read_overlap(unsigned long pfn)
+{
+ int overlap = 0, i;
+
+ for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)
+ if (radix_tree_tag_get(&dma_active_pfn, pfn, i))
+ overlap |= 1 << i;
+ return overlap;
+}
+
+static int active_pfn_set_overlap(unsigned long pfn, int overlap)
+{
+ int i;
+
+ if (overlap > ACTIVE_PFN_MAX_OVERLAP || overlap < 0)
+ return 0;
+
+ for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)
+ if (overlap & 1 << i)
+ radix_tree_tag_set(&dma_active_pfn, pfn, i);
+ else
+ radix_tree_tag_clear(&dma_active_pfn, pfn, i);
+
+ return overlap;
+}
+
+static void active_pfn_inc_overlap(unsigned long pfn)
+{
+ int overlap = active_pfn_read_overlap(pfn);
+
+ overlap = active_pfn_set_overlap(pfn, ++overlap);
+
+ /* If we overflowed the overlap counter then we're potentially
+ * leaking dma-mappings. Otherwise, if maps and unmaps are
+ * balanced then this overflow may cause false negatives in
+ * debug_dma_assert_idle() as the pfn may be marked idle
+ * prematurely.
+ */
+ WARN_ONCE(overlap == 0,
+ "DMA-API: exceeded %d overlapping mappings of pfn %lx\n",
+ ACTIVE_PFN_MAX_OVERLAP, pfn);
+}
+
+static int active_pfn_dec_overlap(unsigned long pfn)
+{
+ int overlap = active_pfn_read_overlap(pfn);
+
+ return active_pfn_set_overlap(pfn, --overlap);
+}
+
+static int active_pfn_insert(struct dma_debug_entry *entry)
+{
+ unsigned long flags;
+ int rc;
+
+ spin_lock_irqsave(&radix_lock, flags);
+ rc = radix_tree_insert(&dma_active_pfn, entry->pfn, entry);
+ if (rc == -EEXIST)
+ active_pfn_inc_overlap(entry->pfn);
+ spin_unlock_irqrestore(&radix_lock, flags);
+
+ return rc;
+}
+
+static void active_pfn_remove(struct dma_debug_entry *entry)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&radix_lock, flags);
+ if (active_pfn_dec_overlap(entry->pfn) == 0)
+ radix_tree_delete(&dma_active_pfn, entry->pfn);
+ spin_unlock_irqrestore(&radix_lock, flags);
+}
+
+/**
+ * debug_dma_assert_idle() - assert that a page is not undergoing dma
+ * @page: page to lookup in the dma_active_pfn tree
+ *
+ * Place a call to this routine in cases where the cpu touching the page
+ * before the dma completes (page is dma_unmapped) will lead to data
+ * corruption.
+ */
+void debug_dma_assert_idle(struct page *page)
+{
+ unsigned long flags;
+ struct dma_debug_entry *entry;
+
+ if (!page)
+ return;
+
+ spin_lock_irqsave(&radix_lock, flags);
+ entry = radix_tree_lookup(&dma_active_pfn, page_to_pfn(page));
+ spin_unlock_irqrestore(&radix_lock, flags);
+
+ if (!entry)
+ return;
+
+ err_printk(entry->dev, entry,
+ "DMA-API: cpu touching an active dma mapped page "
+ "[pfn=0x%lx]\n", entry->pfn);
+}
+
+/*
* Wrapper function for adding an entry to the hash.
* This function takes care of locking itself.
*/
@@ -411,10 +558,21 @@ static void add_dma_entry(struct dma_debug_entry *entry)
{
struct hash_bucket *bucket;
unsigned long flags;
+ int rc;
bucket = get_hash_bucket(entry, &flags);
hash_bucket_add(bucket, entry);
put_hash_bucket(bucket, &flags);
+
+ rc = active_pfn_insert(entry);
+ if (rc == -ENOMEM) {
+ pr_err("DMA-API: pfn tracking ENOMEM, dma-debug disabled\n");
+ global_disable = true;
+ }
+
+ /* TODO: report -EEXIST errors here as overlapping mappings are
+ * not supported by the DMA API
+ */
}
static struct dma_debug_entry *__dma_entry_alloc(void)
@@ -469,6 +627,8 @@ static void dma_entry_free(struct dma_debug_entry *entry)
{
unsigned long flags;
+ active_pfn_remove(entry);
+
/*
* add to beginning of the list - this way the entries are
* more likely cache hot when they are reallocated.
@@ -895,15 +1055,15 @@ static void check_unmap(struct dma_debug_entry *ref)
ref->dev_addr, ref->size,
type2name[entry->type], type2name[ref->type]);
} else if ((entry->type == dma_debug_coherent) &&
- (ref->paddr != entry->paddr)) {
+ (phys_addr(ref) != phys_addr(entry))) {
err_printk(ref->dev, entry, "DMA-API: device driver frees "
"DMA memory with different CPU address "
"[device address=0x%016llx] [size=%llu bytes] "
"[cpu alloc address=0x%016llx] "
"[cpu free address=0x%016llx]",
ref->dev_addr, ref->size,
- (unsigned long long)entry->paddr,
- (unsigned long long)ref->paddr);
+ phys_addr(entry),
+ phys_addr(ref));
}
if (ref->sg_call_ents && ref->type == dma_debug_sg &&
@@ -1052,7 +1212,8 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
entry->dev = dev;
entry->type = dma_debug_page;
- entry->paddr = page_to_phys(page) + offset;
+ entry->pfn = page_to_pfn(page);
+ entry->offset = offset,
entry->dev_addr = dma_addr;
entry->size = size;
entry->direction = direction;
@@ -1148,7 +1309,8 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
entry->type = dma_debug_sg;
entry->dev = dev;
- entry->paddr = sg_phys(s);
+ entry->pfn = page_to_pfn(sg_page(s));
+ entry->offset = s->offset,
entry->size = sg_dma_len(s);
entry->dev_addr = sg_dma_address(s);
entry->direction = direction;
@@ -1198,7 +1360,8 @@ void debug_dma_unmap_sg(struct device *dev, struct scatterlist *sglist,
struct dma_debug_entry ref = {
.type = dma_debug_sg,
.dev = dev,
- .paddr = sg_phys(s),
+ .pfn = page_to_pfn(sg_page(s)),
+ .offset = s->offset,
.dev_addr = sg_dma_address(s),
.size = sg_dma_len(s),
.direction = dir,
@@ -1233,7 +1396,8 @@ void debug_dma_alloc_coherent(struct device *dev, size_t size,
entry->type = dma_debug_coherent;
entry->dev = dev;
- entry->paddr = virt_to_phys(virt);
+ entry->pfn = page_to_pfn(virt_to_page(virt));
+ entry->offset = (size_t) virt & PAGE_MASK;
entry->size = size;
entry->dev_addr = dma_addr;
entry->direction = DMA_BIDIRECTIONAL;
@@ -1248,7 +1412,8 @@ void debug_dma_free_coherent(struct device *dev, size_t size,
struct dma_debug_entry ref = {
.type = dma_debug_coherent,
.dev = dev,
- .paddr = virt_to_phys(virt),
+ .pfn = page_to_pfn(virt_to_page(virt)),
+ .offset = (size_t) virt & PAGE_MASK,
.dev_addr = addr,
.size = size,
.direction = DMA_BIDIRECTIONAL,
@@ -1356,7 +1521,8 @@ void debug_dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
struct dma_debug_entry ref = {
.type = dma_debug_sg,
.dev = dev,
- .paddr = sg_phys(s),
+ .pfn = page_to_pfn(sg_page(s)),
+ .offset = s->offset,
.dev_addr = sg_dma_address(s),
.size = sg_dma_len(s),
.direction = direction,
@@ -1388,7 +1554,8 @@ void debug_dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
struct dma_debug_entry ref = {
.type = dma_debug_sg,
.dev = dev,
- .paddr = sg_phys(s),
+ .pfn = page_to_pfn(sg_page(s)),
+ .offset = s->offset,
.dev_addr = sg_dma_address(s),
.size = sg_dma_len(s),
.direction = direction,
diff --git a/mm/memory.c b/mm/memory.c
index 5d9025f3b3e1..c89788436f81 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -59,6 +59,7 @@
#include <linux/gfp.h>
#include <linux/migrate.h>
#include <linux/string.h>
+#include <linux/dma-debug.h>
#include <asm/io.h>
#include <asm/pgalloc.h>
@@ -2559,6 +2560,8 @@ static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
{
+ debug_dma_assert_idle(src);
+
/*
* If the source page was a PFN mapping, we don't have
* a "struct page" for it. We do a best-effort copy by
--
1.7.7.6
--
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