[PATCH 6.18 063/198] dma-debug: track cache clean flag in entries

Greg Kroah-Hartman
2026-04-20T15:58:46Z

From: Michael S. Tsirkin <mst@redhat.com>

[ Upstream commit d5d846513128c1a3bc2f2d371f6e903177dea443 ]

If a driver is buggy and has 2 overlapping mappings but only
sets cache clean flag on the 1st one of them, we warn.
But if it only does it for the 2nd one, we don't.

Fix by tracking cache clean flag in the entry.

Message-ID: <0ffb3513d18614539c108b4548cdfbc64274a7d1.1767601130.git.mst@redhat.com>
Reviewed-by: Petr Tesarik <ptesarik@suse.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Stable-dep-of: 3d48c9fd78dd ("dma-debug: suppress cacheline overlap warning when arch has no DMA alignment requirement")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/dma/debug.c | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 7e66d863d573f..43d6a996d7a78 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -63,6 +63,7 @@ enum map_err_types {
* @sg_mapped_ents: 'mapped_ents' from dma_map_sg
* @paddr: physical start address of the mapping
* @map_err_type: track whether dma_mapping_error() was checked
+ * @is_cache_clean: driver promises not to write to buffer while mapped
* @stack_len: number of backtrace entries in @stack_entries
* @stack_entries: stack of backtrace history
*/
@@ -76,7 +77,8 @@ struct dma_debug_entry {
int sg_call_ents;
int sg_mapped_ents;
phys_addr_t paddr;
- enum map_err_types map_err_type;
+ enum map_err_types map_err_type;
+ bool is_cache_clean;
#ifdef CONFIG_STACKTRACE
unsigned int stack_len;
unsigned long stack_entries[DMA_DEBUG_STACKTRACE_ENTRIES];
@@ -472,12 +474,15 @@ static int active_cacheline_dec_overlap(phys_addr_t cln)
return active_cacheline_set_overlap(cln, --overlap);
}

-static int active_cacheline_insert(struct dma_debug_entry *entry)
+static int active_cacheline_insert(struct dma_debug_entry *entry,
+ bool *overlap_cache_clean)
{
phys_addr_t cln = to_cacheline_number(entry);
unsigned long flags;
int rc;

+ *overlap_cache_clean = false;
+
/* If the device is not writing memory then we don't have any
* concerns about the cpu consuming stale data. This mitigates
* legitimate usages of overlapping mappings.
@@ -487,8 +492,16 @@ static int active_cacheline_insert(struct dma_debug_entry *entry)

spin_lock_irqsave(&radix_lock, flags);
rc = radix_tree_insert(&dma_active_cacheline, cln, entry);
- if (rc == -EEXIST)
+ if (rc == -EEXIST) {
+ struct dma_debug_entry *existing;
+
active_cacheline_inc_overlap(cln);
+ existing = radix_tree_lookup(&dma_active_cacheline, cln);
+ /* A lookup failure here after we got -EEXIST is unexpected. */
+ WARN_ON(!existing);
+ if (existing)
+ *overlap_cache_clean = existing->is_cache_clean;
+ }
spin_unlock_irqrestore(&radix_lock, flags);

return rc;
@@ -583,20 +596,24 @@ DEFINE_SHOW_ATTRIBUTE(dump);
*/
static void add_dma_entry(struct dma_debug_entry *entry, unsigned long attrs)
{
+ bool overlap_cache_clean;
struct hash_bucket *bucket;
unsigned long flags;
int rc;

+ entry->is_cache_clean = !!(attrs & DMA_ATTR_CPU_CACHE_CLEAN);
+
bucket = get_hash_bucket(entry, &flags);
hash_bucket_add(bucket, entry);
put_hash_bucket(bucket, flags);

- rc = active_cacheline_insert(entry);
+ rc = active_cacheline_insert(entry, &overlap_cache_clean);
if (rc == -ENOMEM) {
pr_err_once("cacheline tracking ENOMEM, dma-debug disabled\n");
global_disable = true;
} else if (rc == -EEXIST &&
- !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_CPU_CACHE_CLEAN)) &&
+ !(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
+ !(entry->is_cache_clean && overlap_cache_clean) &&
!(IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) &&
is_swiotlb_active(entry->dev))) {
err_printk(entry->dev, entry,
--
2.53.0