[PATCH v3 0/8] RDMA: Enable operation with DMA debug enabled

[PATCH v3 0/8] RDMA: Enable operation with DMA debug enabled

[Leon Romanovsky]

Add a new DMA_ATTR_REQUIRE_COHERENT attribute to the DMA API to mark
mappings that must run on a DMA‑coherent system. Such buffers cannot
use the SWIOTLB path, may overlap with CPU caches, and do not depend on
explicit cache flushing.

Mappings using this attribute are rejected on systems where cache
side‑effects could lead to data corruption, and therefore do not need
the cache‑overlap debugging logic. This series also includes fixes for
DMA_ATTR_CPU_CACHE_CLEAN handling.
Thanks.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
Changes in v3:
- Enriched commit messages and documentation
- Added ROB tags
- Link to v2: https://patch.msgid.link/20260311-dma-debug-overlap-v2-0-e00bc2ca346d@nvidia.com

Changes in v2:
- Added DMA_ATTR_REQUIRE_COHERENT attribute
- Added HMM patch which needs this attribute as well
- Renamed DMA_ATTR_CPU_CACHE_CLEAN to be DMA_ATTR_DEBUGGING_IGNORE_CACHELINES
- Link to v1: https://patch.msgid.link/20260307-dma-debug-overlap-v1-0-c034c38872af@nvidia.com

---
Leon Romanovsky (8):
      dma-debug: Allow multiple invocations of overlapping entries
      dma-mapping: handle DMA_ATTR_CPU_CACHE_CLEAN in trace output
      dma-mapping: Clarify valid conditions for CPU cache line overlap
      dma-mapping: Introduce DMA require coherency attribute
      dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set
      iommu/dma: add support for DMA_ATTR_REQUIRE_COHERENT attribute
      RDMA/umem: Tell DMA mapping that UMEM requires coherency
      mm/hmm: Indicate that HMM requires DMA coherency

 Documentation/core-api/dma-attributes.rst | 38 ++++++++++++++++++++++++-------
 drivers/infiniband/core/umem.c            |  5 ++--
 drivers/iommu/dma-iommu.c                 | 21 +++++++++++++----
 drivers/virtio/virtio_ring.c              | 10 ++++----
 include/linux/dma-mapping.h               | 15 ++++++++----
 include/trace/events/dma.h                |  4 +++-
 kernel/dma/debug.c                        |  9 ++++----
 kernel/dma/direct.h                       |  7 +++---
 kernel/dma/mapping.c                      |  6 +++++
 mm/hmm.c                                  |  4 ++--
 10 files changed, 86 insertions(+), 33 deletions(-)
---
base-commit: 11439c4635edd669ae435eec308f4ab8a0804808
change-id: 20260305-dma-debug-overlap-21487c3fa02c

Best regards,
--  
Leon Romanovsky <leonro@nvidia.com>

[PATCH v3 1/8] dma-debug: Allow multiple invocations of overlapping entries

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

Repeated DMA mappings with DMA_ATTR_CPU_CACHE_CLEAN trigger the
following splat. This prevents using the attribute in cases where a DMA
region is shared and reused more than seven times.

 ------------[ cut here ]------------
 DMA-API: exceeded 7 overlapping mappings of cacheline 0x000000000438c440
 WARNING: kernel/dma/debug.c:467 at add_dma_entry+0x219/0x280, CPU#4: ibv_rc_pingpong/1644
 Modules linked in: xt_conntrack xt_MASQUERADE nf_conntrack_netlink nfnetlink iptable_nat nf_nat xt_addrtype br_netfilter rpcsec_gss_krb5 auth_rpcgss oid_registry overlay mlx5_fwctl zram zsmalloc mlx5_ib fuse rpcrdma rdma_ucm ib_uverbs ib_iser libiscsi scsi_transport_iscsi ib_umad rdma_cm ib_ipoib iw_cm ib_cm mlx5_core ib_core
 CPU: 4 UID: 2733 PID: 1644 Comm: ibv_rc_pingpong Not tainted 6.19.0+ #129 PREEMPT
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
 RIP: 0010:add_dma_entry+0x221/0x280
 Code: c0 0f 84 f2 fe ff ff 83 e8 01 89 05 6d 99 11 01 e9 e4 fe ff ff 0f 8e 1f ff ff ff 48 8d 3d 07 ef 2d 01 be 07 00 00 00 48 89 e2 <67> 48 0f b9 3a e9 06 ff ff ff 48 c7 c7 98 05 2b 82 c6 05 72 92 28
 RSP: 0018:ff1100010e657970 EFLAGS: 00010002
 RAX: 0000000000000007 RBX: ff1100010234eb00 RCX: 0000000000000000
 RDX: ff1100010e657970 RSI: 0000000000000007 RDI: ffffffff82678660
 RBP: 000000000438c440 R08: 0000000000000228 R09: 0000000000000000
 R10: 00000000000001be R11: 000000000000089d R12: 0000000000000800
 R13: 00000000ffffffef R14: 0000000000000202 R15: ff1100010234eb00
 FS:  00007fb15f3f6740(0000) GS:ff110008dcc19000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007fb15f32d3a0 CR3: 0000000116f59001 CR4: 0000000000373eb0
 Call Trace:
  <TASK>
  debug_dma_map_sg+0x1b4/0x390
  __dma_map_sg_attrs+0x6d/0x1a0
  dma_map_sgtable+0x19/0x30
  ib_umem_get+0x284/0x3b0 [ib_uverbs]
  mlx5_ib_reg_user_mr+0x68/0x2a0 [mlx5_ib]
  ib_uverbs_reg_mr+0x17f/0x2a0 [ib_uverbs]
  ib_uverbs_handler_UVERBS_METHOD_INVOKE_WRITE+0xc2/0x130 [ib_uverbs]
  ib_uverbs_cmd_verbs+0xa0b/0xae0 [ib_uverbs]
  ? ib_uverbs_handler_UVERBS_METHOD_QUERY_PORT_SPEED+0xe0/0xe0 [ib_uverbs]
  ? mmap_region+0x7a/0xb0
  ? do_mmap+0x3b8/0x5c0
  ib_uverbs_ioctl+0xa7/0x110 [ib_uverbs]
  __x64_sys_ioctl+0x14f/0x8b0
  ? ksys_mmap_pgoff+0xc5/0x190
  do_syscall_64+0x8c/0xbf0
  entry_SYSCALL_64_after_hwframe+0x4b/0x53
 RIP: 0033:0x7fb15f5e4eed
 Code: 04 25 28 00 00 00 48 89 45 c8 31 c0 48 8d 45 10 c7 45 b0 10 00 00 00 48 89 45 b8 48 8d 45 d0 48 89 45 c0 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1a 48 8b 45 c8 64 48 2b 04 25 28 00 00 00
 RSP: 002b:00007ffe09a5c540 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
 RAX: ffffffffffffffda RBX: 00007ffe09a5c5d0 RCX: 00007fb15f5e4eed
 RDX: 00007ffe09a5c5f0 RSI: 00000000c0181b01 RDI: 0000000000000003
 RBP: 00007ffe09a5c590 R08: 0000000000000028 R09: 00007ffe09a5c794
 R10: 0000000000000001 R11: 0000000000000246 R12: 00007ffe09a5c794
 R13: 000000000000000c R14: 0000000025a49170 R15: 000000000000000c
  </TASK>
 ---[ end trace 0000000000000000 ]---

Fixes: 61868dc55a11 ("dma-mapping: add DMA_ATTR_CPU_CACHE_CLEAN")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 kernel/dma/debug.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 86f87e43438c3..be207be749968 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -453,7 +453,7 @@ static int active_cacheline_set_overlap(phys_addr_t cln, int overlap)
 	return overlap;
 }
 
-static void active_cacheline_inc_overlap(phys_addr_t cln)
+static void active_cacheline_inc_overlap(phys_addr_t cln, bool is_cache_clean)
 {
 	int overlap = active_cacheline_read_overlap(cln);
 
@@ -462,7 +462,7 @@ static void active_cacheline_inc_overlap(phys_addr_t cln)
 	/* If we overflowed the overlap counter then we're potentially
 	 * leaking dma-mappings.
 	 */
-	WARN_ONCE(overlap > ACTIVE_CACHELINE_MAX_OVERLAP,
+	WARN_ONCE(!is_cache_clean && overlap > ACTIVE_CACHELINE_MAX_OVERLAP,
 		  pr_fmt("exceeded %d overlapping mappings of cacheline %pa\n"),
 		  ACTIVE_CACHELINE_MAX_OVERLAP, &cln);
 }
@@ -495,7 +495,7 @@ static int active_cacheline_insert(struct dma_debug_entry *entry,
 	if (rc == -EEXIST) {
 		struct dma_debug_entry *existing;
 
-		active_cacheline_inc_overlap(cln);
+		active_cacheline_inc_overlap(cln, entry->is_cache_clean);
 		existing = radix_tree_lookup(&dma_active_cacheline, cln);
 		/* A lookup failure here after we got -EEXIST is unexpected. */
 		WARN_ON(!existing);

-- 
2.53.0

[PATCH v3 2/8] dma-mapping: handle DMA_ATTR_CPU_CACHE_CLEAN in trace output

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

Tracing prints decoded DMA attribute flags, but it does not yet
include the recently added DMA_ATTR_CPU_CACHE_CLEAN. Add support
for decoding and displaying this attribute in the trace output.

Fixes: 61868dc55a11 ("dma-mapping: add DMA_ATTR_CPU_CACHE_CLEAN")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 include/trace/events/dma.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h
index 33e99e792f1aa..69cb3805ee81c 100644
--- a/include/trace/events/dma.h
+++ b/include/trace/events/dma.h
@@ -32,7 +32,8 @@ TRACE_DEFINE_ENUM(DMA_NONE);
 		{ DMA_ATTR_ALLOC_SINGLE_PAGES, "ALLOC_SINGLE_PAGES" }, \
 		{ DMA_ATTR_NO_WARN, "NO_WARN" }, \
 		{ DMA_ATTR_PRIVILEGED, "PRIVILEGED" }, \
-		{ DMA_ATTR_MMIO, "MMIO" })
+		{ DMA_ATTR_MMIO, "MMIO" }, \
+		{ DMA_ATTR_CPU_CACHE_CLEAN, "CACHE_CLEAN" })
 
 DECLARE_EVENT_CLASS(dma_map,
 	TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr,

-- 
2.53.0

[PATCH v3 3/8] dma-mapping: Clarify valid conditions for CPU cache line overlap

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

Rename the DMA_ATTR_CPU_CACHE_CLEAN attribute to better reflect that it
is debugging aid to inform DMA core code that CPU cache line overlaps are
allowed, and refine the documentation describing its use.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 Documentation/core-api/dma-attributes.rst | 22 ++++++++++++++--------
 drivers/virtio/virtio_ring.c              | 10 +++++-----
 include/linux/dma-mapping.h               |  8 ++++----
 include/trace/events/dma.h                |  2 +-
 kernel/dma/debug.c                        |  2 +-
 5 files changed, 25 insertions(+), 19 deletions(-)

diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst
index 1d7bfad73b1c7..48cfe86cc06d7 100644
--- a/Documentation/core-api/dma-attributes.rst
+++ b/Documentation/core-api/dma-attributes.rst
@@ -149,11 +149,17 @@ For architectures that require cache flushing for DMA coherence
 DMA_ATTR_MMIO will not perform any cache flushing. The address
 provided must never be mapped cacheable into the CPU.
 
-DMA_ATTR_CPU_CACHE_CLEAN
-------------------------
-
-This attribute indicates the CPU will not dirty any cacheline overlapping this
-DMA_FROM_DEVICE/DMA_BIDIRECTIONAL buffer while it is mapped. This allows
-multiple small buffers to safely share a cacheline without risk of data
-corruption, suppressing DMA debug warnings about overlapping mappings.
-All mappings sharing a cacheline should have this attribute.
+DMA_ATTR_DEBUGGING_IGNORE_CACHELINES
+------------------------------------
+
+This attribute indicates that CPU cache lines may overlap for buffers mapped
+with DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
+
+Such overlap may occur when callers map multiple small buffers that reside
+within the same cache line. In this case, callers must guarantee that the CPU
+will not dirty these cache lines after the mappings are established. When this
+condition is met, multiple buffers can safely share a cache line without risking
+data corruption.
+
+All mappings that share a cache line must set this attribute to suppress DMA
+debug warnings about overlapping mappings.
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 335692d41617a..fbca7ce1c6bf0 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2912,10 +2912,10 @@ EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);
  * @data: the token identifying the buffer.
  * @gfp: how to do memory allocations (if necessary).
  *
- * Same as virtqueue_add_inbuf but passes DMA_ATTR_CPU_CACHE_CLEAN to indicate
- * that the CPU will not dirty any cacheline overlapping this buffer while it
- * is available, and to suppress overlapping cacheline warnings in DMA debug
- * builds.
+ * Same as virtqueue_add_inbuf but passes DMA_ATTR_DEBUGGING_IGNORE_CACHELINES
+ * to indicate that the CPU will not dirty any cacheline overlapping this buffer
+ * while it is available, and to suppress overlapping cacheline warnings in DMA
+ * debug builds.
  *
  * Caller must ensure we don't call this with other virtqueue operations
  * at the same time (except where noted).
@@ -2928,7 +2928,7 @@ int virtqueue_add_inbuf_cache_clean(struct virtqueue *vq,
 				    gfp_t gfp)
 {
 	return virtqueue_add(vq, &sg, num, 0, 1, data, NULL, false, gfp,
-			     DMA_ATTR_CPU_CACHE_CLEAN);
+			     DMA_ATTR_DEBUGGING_IGNORE_CACHELINES);
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_cache_clean);
 
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 29973baa05816..da44394b3a1a7 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -80,11 +80,11 @@
 #define DMA_ATTR_MMIO		(1UL << 10)
 
 /*
- * DMA_ATTR_CPU_CACHE_CLEAN: Indicates the CPU will not dirty any cacheline
- * overlapping this buffer while it is mapped for DMA. All mappings sharing
- * a cacheline must have this attribute for this to be considered safe.
+ * DMA_ATTR_DEBUGGING_IGNORE_CACHELINES: Indicates the CPU cache line can be
+ * overlapped. All mappings sharing a cacheline must have this attribute for
+ * this to be considered safe.
  */
-#define DMA_ATTR_CPU_CACHE_CLEAN	(1UL << 11)
+#define DMA_ATTR_DEBUGGING_IGNORE_CACHELINES	(1UL << 11)
 
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.  It can
diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h
index 69cb3805ee81c..8c64bc0721fe4 100644
--- a/include/trace/events/dma.h
+++ b/include/trace/events/dma.h
@@ -33,7 +33,7 @@ TRACE_DEFINE_ENUM(DMA_NONE);
 		{ DMA_ATTR_NO_WARN, "NO_WARN" }, \
 		{ DMA_ATTR_PRIVILEGED, "PRIVILEGED" }, \
 		{ DMA_ATTR_MMIO, "MMIO" }, \
-		{ DMA_ATTR_CPU_CACHE_CLEAN, "CACHE_CLEAN" })
+		{ DMA_ATTR_DEBUGGING_IGNORE_CACHELINES, "CACHELINES_OVERLAP" })
 
 DECLARE_EVENT_CLASS(dma_map,
 	TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr,
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index be207be749968..83e1cfe05f08d 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -601,7 +601,7 @@ static void add_dma_entry(struct dma_debug_entry *entry, unsigned long attrs)
 	unsigned long flags;
 	int rc;
 
-	entry->is_cache_clean = !!(attrs & DMA_ATTR_CPU_CACHE_CLEAN);
+	entry->is_cache_clean = attrs & DMA_ATTR_DEBUGGING_IGNORE_CACHELINES;
 
 	bucket = get_hash_bucket(entry, &flags);
 	hash_bucket_add(bucket, entry);

-- 
2.53.0

[PATCH v3 4/8] dma-mapping: Introduce DMA require coherency attribute

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

The mapping buffers which carry this attribute require DMA coherent system.
This means that they can't take SWIOTLB path, can perform CPU cache overlap
and doesn't perform cache flushing.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 Documentation/core-api/dma-attributes.rst | 16 ++++++++++++++++
 include/linux/dma-mapping.h               |  7 +++++++
 include/trace/events/dma.h                |  3 ++-
 kernel/dma/debug.c                        |  3 ++-
 kernel/dma/mapping.c                      |  6 ++++++
 5 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst
index 48cfe86cc06d7..441bdc9d08318 100644
--- a/Documentation/core-api/dma-attributes.rst
+++ b/Documentation/core-api/dma-attributes.rst
@@ -163,3 +163,19 @@ data corruption.
 
 All mappings that share a cache line must set this attribute to suppress DMA
 debug warnings about overlapping mappings.
+
+DMA_ATTR_REQUIRE_COHERENT
+-------------------------
+
+DMA mapping requests with the DMA_ATTR_REQUIRE_COHERENT fail on any
+system where SWIOTLB or cache management is required. This should only
+be used to support uAPI designs that require continuous HW DMA
+coherence with userspace processes, for example RDMA and DRM. At a
+minimum the memory being mapped must be userspace memory from
+pin_user_pages() or similar.
+
+Drivers should consider using dma_mmap_pages() instead of this
+interface when building their uAPIs, when possible.
+
+It must never be used in an in-kernel driver that only works with
+kernal memory.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index da44394b3a1a7..482b919f040f7 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -86,6 +86,13 @@
  */
 #define DMA_ATTR_DEBUGGING_IGNORE_CACHELINES	(1UL << 11)
 
+/*
+ * DMA_ATTR_REQUIRE_COHERENT: Indicates that DMA coherency is required.
+ * All mappings that carry this attribute can't work with SWIOTLB and cache
+ * flushing.
+ */
+#define DMA_ATTR_REQUIRE_COHERENT	(1UL << 12)
+
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.  It can
  * be given to a device to use as a DMA source or target.  It is specific to a
diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h
index 8c64bc0721fe4..63597b0044247 100644
--- a/include/trace/events/dma.h
+++ b/include/trace/events/dma.h
@@ -33,7 +33,8 @@ TRACE_DEFINE_ENUM(DMA_NONE);
 		{ DMA_ATTR_NO_WARN, "NO_WARN" }, \
 		{ DMA_ATTR_PRIVILEGED, "PRIVILEGED" }, \
 		{ DMA_ATTR_MMIO, "MMIO" }, \
-		{ DMA_ATTR_DEBUGGING_IGNORE_CACHELINES, "CACHELINES_OVERLAP" })
+		{ DMA_ATTR_DEBUGGING_IGNORE_CACHELINES, "CACHELINES_OVERLAP" }, \
+		{ DMA_ATTR_REQUIRE_COHERENT, "REQUIRE_COHERENT" })
 
 DECLARE_EVENT_CLASS(dma_map,
 	TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr,
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 83e1cfe05f08d..0677918f06a80 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -601,7 +601,8 @@ static void add_dma_entry(struct dma_debug_entry *entry, unsigned long attrs)
 	unsigned long flags;
 	int rc;
 
-	entry->is_cache_clean = attrs & DMA_ATTR_DEBUGGING_IGNORE_CACHELINES;
+	entry->is_cache_clean = attrs & (DMA_ATTR_DEBUGGING_IGNORE_CACHELINES |
+					 DMA_ATTR_REQUIRE_COHERENT);
 
 	bucket = get_hash_bucket(entry, &flags);
 	hash_bucket_add(bucket, entry);
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 3928a509c44c2..6d3dd0bd3a886 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -164,6 +164,9 @@ dma_addr_t dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
 	if (WARN_ON_ONCE(!dev->dma_mask))
 		return DMA_MAPPING_ERROR;
 
+	if (!dev_is_dma_coherent(dev) && (attrs & DMA_ATTR_REQUIRE_COHERENT))
+		return DMA_MAPPING_ERROR;
+
 	if (dma_map_direct(dev, ops) ||
 	    (!is_mmio && arch_dma_map_phys_direct(dev, phys + size)))
 		addr = dma_direct_map_phys(dev, phys, size, dir, attrs);
@@ -235,6 +238,9 @@ static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
 
 	BUG_ON(!valid_dma_direction(dir));
 
+	if (!dev_is_dma_coherent(dev) && (attrs & DMA_ATTR_REQUIRE_COHERENT))
+		return -EOPNOTSUPP;
+
 	if (WARN_ON_ONCE(!dev->dma_mask))
 		return 0;
 

-- 
2.53.0

Re: [PATCH v3 4/8] dma-mapping: Introduce DMA require coherency attribute

[Randy Dunlap]

On 3/16/26 12:06 PM, Leon Romanovsky wrote:
> diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst
> index 48cfe86cc06d7..441bdc9d08318 100644
> --- a/Documentation/core-api/dma-attributes.rst
> +++ b/Documentation/core-api/dma-attributes.rst
> @@ -163,3 +163,19 @@ data corruption.
>  
>  All mappings that share a cache line must set this attribute to suppress DMA
>  debug warnings about overlapping mappings.
> +
> +DMA_ATTR_REQUIRE_COHERENT
> +-------------------------
> +
> +DMA mapping requests with the DMA_ATTR_REQUIRE_COHERENT fail on any
> +system where SWIOTLB or cache management is required. This should only
> +be used to support uAPI designs that require continuous HW DMA
> +coherence with userspace processes, for example RDMA and DRM. At a
> +minimum the memory being mapped must be userspace memory from
> +pin_user_pages() or similar.
> +
> +Drivers should consider using dma_mmap_pages() instead of this
> +interface when building their uAPIs, when possible.
> +
> +It must never be used in an in-kernel driver that only works with
> +kernal memory.

   kernel

-- 
~Randy

Re: [PATCH v3 4/8] dma-mapping: Introduce DMA require coherency attribute

[Leon Romanovsky]

On Mon, Mar 16, 2026 at 12:17:39PM -0700, Randy Dunlap wrote:
> 
> 
> On 3/16/26 12:06 PM, Leon Romanovsky wrote:
> > diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst
> > index 48cfe86cc06d7..441bdc9d08318 100644
> > --- a/Documentation/core-api/dma-attributes.rst
> > +++ b/Documentation/core-api/dma-attributes.rst
> > @@ -163,3 +163,19 @@ data corruption.
> >  
> >  All mappings that share a cache line must set this attribute to suppress DMA
> >  debug warnings about overlapping mappings.
> > +
> > +DMA_ATTR_REQUIRE_COHERENT
> > +-------------------------
> > +
> > +DMA mapping requests with the DMA_ATTR_REQUIRE_COHERENT fail on any
> > +system where SWIOTLB or cache management is required. This should only
> > +be used to support uAPI designs that require continuous HW DMA
> > +coherence with userspace processes, for example RDMA and DRM. At a
> > +minimum the memory being mapped must be userspace memory from
> > +pin_user_pages() or similar.
> > +
> > +Drivers should consider using dma_mmap_pages() instead of this
> > +interface when building their uAPIs, when possible.
> > +
> > +It must never be used in an in-kernel driver that only works with
> > +kernal memory.
> 
>    kernel

Thanks, let's hope that it is the only one comment :).

> 
> -- 
> ~Randy
> 

[PATCH v3 5/8] dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

DMA_ATTR_REQUIRE_COHERENT indicates that SWIOTLB must not be used.
Ensure the SWIOTLB path is declined whenever the DMA direct path is
selected.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 kernel/dma/direct.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
index e89f175e9c2d0..6184ff303f080 100644
--- a/kernel/dma/direct.h
+++ b/kernel/dma/direct.h
@@ -84,7 +84,7 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
 	dma_addr_t dma_addr;
 
 	if (is_swiotlb_force_bounce(dev)) {
-		if (attrs & DMA_ATTR_MMIO)
+		if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
 			return DMA_MAPPING_ERROR;
 
 		return swiotlb_map(dev, phys, size, dir, attrs);
@@ -98,7 +98,8 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
 		dma_addr = phys_to_dma(dev, phys);
 		if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
 		    dma_kmalloc_needs_bounce(dev, size, dir)) {
-			if (is_swiotlb_active(dev))
+			if (is_swiotlb_active(dev) &&
+			    !(attrs & DMA_ATTR_REQUIRE_COHERENT))
 				return swiotlb_map(dev, phys, size, dir, attrs);
 
 			goto err_overflow;
@@ -123,7 +124,7 @@ static inline void dma_direct_unmap_phys(struct device *dev, dma_addr_t addr,
 {
 	phys_addr_t phys;
 
-	if (attrs & DMA_ATTR_MMIO)
+	if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
 		/* nothing to do: uncached and no swiotlb */
 		return;
 

-- 
2.53.0

[PATCH v3 6/8] iommu/dma: add support for DMA_ATTR_REQUIRE_COHERENT attribute

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

Add support for the DMA_ATTR_REQUIRE_COHERENT attribute to the exported
functions. This attribute indicates that the SWIOTLB path must not be
used and that no sync operations should be performed.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/iommu/dma-iommu.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 5dac64be61bb2..94d5141696424 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1211,7 +1211,7 @@ dma_addr_t iommu_dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
 	 */
 	if (dev_use_swiotlb(dev, size, dir) &&
 	    iova_unaligned(iovad, phys, size)) {
-		if (attrs & DMA_ATTR_MMIO)
+		if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
 			return DMA_MAPPING_ERROR;
 
 		phys = iommu_dma_map_swiotlb(dev, phys, size, dir, attrs);
@@ -1223,7 +1223,8 @@ dma_addr_t iommu_dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
 		arch_sync_dma_for_device(phys, size, dir);
 
 	iova = __iommu_dma_map(dev, phys, size, prot, dma_mask);
-	if (iova == DMA_MAPPING_ERROR && !(attrs & DMA_ATTR_MMIO))
+	if (iova == DMA_MAPPING_ERROR &&
+	    !(attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT)))
 		swiotlb_tbl_unmap_single(dev, phys, size, dir, attrs);
 	return iova;
 }
@@ -1233,7 +1234,7 @@ void iommu_dma_unmap_phys(struct device *dev, dma_addr_t dma_handle,
 {
 	phys_addr_t phys;
 
-	if (attrs & DMA_ATTR_MMIO) {
+	if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT)) {
 		__iommu_dma_unmap(dev, dma_handle, size);
 		return;
 	}
@@ -1945,9 +1946,21 @@ int dma_iova_link(struct device *dev, struct dma_iova_state *state,
 	if (WARN_ON_ONCE(iova_start_pad && offset > 0))
 		return -EIO;
 
+	/*
+	 * DMA_IOVA_USE_SWIOTLB is set on state after some entry
+	 * took SWIOTLB path, which we were supposed to prevent
+	 * for DMA_ATTR_REQUIRE_COHERENT attribute.
+	 */
+	if (WARN_ON_ONCE((state->__size & DMA_IOVA_USE_SWIOTLB) &&
+			 (attrs & DMA_ATTR_REQUIRE_COHERENT)))
+		return -EOPNOTSUPP;
+
+	if (!dev_is_dma_coherent(dev) && (attrs & DMA_ATTR_REQUIRE_COHERENT))
+		return -EOPNOTSUPP;
+
 	if (dev_use_swiotlb(dev, size, dir) &&
 	    iova_unaligned(iovad, phys, size)) {
-		if (attrs & DMA_ATTR_MMIO)
+		if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
 			return -EPERM;
 
 		return iommu_dma_iova_link_swiotlb(dev, state, phys, offset,

-- 
2.53.0

[PATCH v3 7/8] RDMA/umem: Tell DMA mapping that UMEM requires coherency

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

The RDMA subsystem exposes DMA regions through the verbs interface, which
assumes a coherent system. Use the DMA_ATTR_REQUIRE_COHERENCE attribute
to ensure coherency and avoid taking the SWIOTLB path.

The RDMA verbs programming model resembles HMM and assumes concurrent DMA
and CPU access to userspace memory. The hardware and programming model
support "one-sided" operations initiated remotely without any local CPU
involvement or notification. These include ATOMIC compare/swap, READ, and
WRITE. A remote CPU can use these operations to traverse data structures,
manipulate locks, and perform similar tasks without the host CPU’s
awareness. If SWIOTLB substitutes memory or DMA is not cache coherent,
these use cases break entirely.

In-kernel RDMA is fine with incoherent mappings because kernel users do
not rely on one-sided operations in ways that would expose these issues.

A given region may also be exported multiple times, which can trigger
warnings about cacheline overlaps. These warnings are suppressed when the
new attribute is used.

infiniband rocep8s0f0: mlx5_ib_reg_user_mr:1592:(pid 5812): start 0x2b28c000, iova 0x2b28c000, length 0x1000, access_flags 0x1
infiniband rocep8s0f0: mlx5_ib_reg_user_mr:1592:(pid 5812): start 0x2b28c001, iova 0x2b28c001, length 0xfff, access_flags 0x1
 ------------[ cut here ]------------
 DMA-API: mlx5_core 0000:08:00.0: cacheline tracking EEXIST, overlapping mappings aren't supported
 WARNING: kernel/dma/debug.c:620 at add_dma_entry+0x1bb/0x280, CPU#6: ibv_rc_pingpong/5812
 Modules linked in: veth xt_conntrack xt_MASQUERADE nf_conntrack_netlink nfnetlink iptable_nat nf_nat xt_addrtype br_netfilter rpcsec_gss_krb5 auth_rpcgss oid_registry overlay mlx5_fwctl zram zsmalloc mlx5_ib fuse rpcrdma rdma_ucm ib_uverbs ib_iser libiscsi scsi_transport_iscsi ib_umad rdma_cm ib_ipoib iw_cm ib_cm mlx5_core ib_core
 CPU: 6 UID: 2733 PID: 5812 Comm: ibv_rc_pingpong Tainted: G        W           6.19.0+ #129 PREEMPT
 Tainted: [W]=WARN
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
 RIP: 0010:add_dma_entry+0x1be/0x280
 Code: 8b 7b 10 48 85 ff 0f 84 c3 00 00 00 48 8b 6f 50 48 85 ed 75 03 48 8b 2f e8 ff 8e 6a 00 48 89 c6 48 8d 3d 55 ef 2d 01 48 89 ea <67> 48 0f b9 3a 48 85 db 74 1a 48 c7 c7 b0 00 2b 82 e8 9c 25 fd ff
 RSP: 0018:ff11000138717978 EFLAGS: 00010286
 RAX: ffffffffa02d7831 RBX: ff1100010246de00 RCX: 0000000000000000
 RDX: ff110001036fac30 RSI: ffffffffa02d7831 RDI: ffffffff82678650
 RBP: ff110001036fac30 R08: ff11000110dcb4a0 R09: ff11000110dcb478
 R10: 0000000000000000 R11: ffffffff824b30a8 R12: 0000000000000000
 R13: 00000000ffffffef R14: 0000000000000202 R15: ff1100010246de00
 FS:  00007f59b411c740(0000) GS:ff110008dcc99000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007ffe538f7000 CR3: 000000010e066005 CR4: 0000000000373eb0
 Call Trace:
  <TASK>
  debug_dma_map_sg+0x1b4/0x390
  __dma_map_sg_attrs+0x6d/0x1a0
  dma_map_sgtable+0x19/0x30
  ib_umem_get+0x254/0x380 [ib_uverbs]
  mlx5_ib_reg_user_mr+0x68/0x2a0 [mlx5_ib]
  ib_uverbs_reg_mr+0x17f/0x2a0 [ib_uverbs]
  ib_uverbs_handler_UVERBS_METHOD_INVOKE_WRITE+0xc2/0x130 [ib_uverbs]
  ib_uverbs_cmd_verbs+0xa0b/0xae0 [ib_uverbs]
  ? ib_uverbs_handler_UVERBS_METHOD_QUERY_PORT_SPEED+0xe0/0xe0 [ib_uverbs]
  ? mmap_region+0x7a/0xb0
  ? do_mmap+0x3b8/0x5c0
  ib_uverbs_ioctl+0xa7/0x110 [ib_uverbs]
  __x64_sys_ioctl+0x14f/0x8b0
  ? ksys_mmap_pgoff+0xc5/0x190
  do_syscall_64+0x8c/0xbf0
  entry_SYSCALL_64_after_hwframe+0x4b/0x53
 RIP: 0033:0x7f59b430aeed
 Code: 04 25 28 00 00 00 48 89 45 c8 31 c0 48 8d 45 10 c7 45 b0 10 00 00 00 48 89 45 b8 48 8d 45 d0 48 89 45 c0 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1a 48 8b 45 c8 64 48 2b 04 25 28 00 00 00
 RSP: 002b:00007ffe538f9430 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
 RAX: ffffffffffffffda RBX: 00007ffe538f94c0 RCX: 00007f59b430aeed
 RDX: 00007ffe538f94e0 RSI: 00000000c0181b01 RDI: 0000000000000003
 RBP: 00007ffe538f9480 R08: 0000000000000028 R09: 00007ffe538f9684
 R10: 0000000000000001 R11: 0000000000000246 R12: 00007ffe538f9684
 R13: 000000000000000c R14: 000000002b28d170 R15: 000000000000000c
  </TASK>
 ---[ end trace 0000000000000000 ]---

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/infiniband/core/umem.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index cff4fcca2c345..edc34c69f0f23 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -55,7 +55,8 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
 
 	if (dirty)
 		ib_dma_unmap_sgtable_attrs(dev, &umem->sgt_append.sgt,
-					   DMA_BIDIRECTIONAL, 0);
+					   DMA_BIDIRECTIONAL,
+					   DMA_ATTR_REQUIRE_COHERENT);
 
 	for_each_sgtable_sg(&umem->sgt_append.sgt, sg, i) {
 		unpin_user_page_range_dirty_lock(sg_page(sg),
@@ -169,7 +170,7 @@ struct ib_umem *ib_umem_get(struct ib_device *device, unsigned long addr,
 	unsigned long lock_limit;
 	unsigned long new_pinned;
 	unsigned long cur_base;
-	unsigned long dma_attr = 0;
+	unsigned long dma_attr = DMA_ATTR_REQUIRE_COHERENT;
 	struct mm_struct *mm;
 	unsigned long npages;
 	int pinned, ret;

-- 
2.53.0

[PATCH v3 8/8] mm/hmm: Indicate that HMM requires DMA coherency

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

HMM is fundamentally about allowing a sophisticated device to perform DMA
directly to a process’s memory while the CPU accesses that same memory at
the same time. It is similar to SVA but does not rely on IOMMU support.
Because the entire model depends on concurrent access to shared memory, it
fails as a uAPI if SWIOTLB substitutes the memory or if the CPU caches are
not coherent with DMA.

Until now, there has been no reliable way to report this, and various
approximations have been used:

int hmm_dma_map_alloc(struct device *dev, struct hmm_dma_map *map,
                      size_t nr_entries, size_t dma_entry_size)
{
<...>
        /*
         * The HMM API violates our normal DMA buffer ownership rules and can't
         * transfer buffer ownership.  The dma_addressing_limited() check is a
         * best approximation to ensure no swiotlb buffering happens.
         */
        dma_need_sync = !dev->dma_skip_sync;
        if (dma_need_sync || dma_addressing_limited(dev))
                return -EOPNOTSUPP;

So let's mark mapped buffers with DMA_ATTR_REQUIRE_COHERENT attribute
to prevent silent data corruption if someone tries to use hmm in a system
with swiotlb or incoherent DMA

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 mm/hmm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index f6c4ddff4bd61..5955f2f0c83db 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -778,7 +778,7 @@ dma_addr_t hmm_dma_map_pfn(struct device *dev, struct hmm_dma_map *map,
 	struct page *page = hmm_pfn_to_page(pfns[idx]);
 	phys_addr_t paddr = hmm_pfn_to_phys(pfns[idx]);
 	size_t offset = idx * map->dma_entry_size;
-	unsigned long attrs = 0;
+	unsigned long attrs = DMA_ATTR_REQUIRE_COHERENT;
 	dma_addr_t dma_addr;
 	int ret;
 
@@ -871,7 +871,7 @@ bool hmm_dma_unmap_pfn(struct device *dev, struct hmm_dma_map *map, size_t idx)
 	struct dma_iova_state *state = &map->state;
 	dma_addr_t *dma_addrs = map->dma_list;
 	unsigned long *pfns = map->pfn_list;
-	unsigned long attrs = 0;
+	unsigned long attrs = DMA_ATTR_REQUIRE_COHERENT;
 
 	if ((pfns[idx] & valid_dma) != valid_dma)
 		return false;

-- 
2.53.0

Re: [PATCH v3 0/8] RDMA: Enable operation with DMA debug enabled

[Leon Romanovsky]

On Mon, Mar 16, 2026 at 09:06:44PM +0200, Leon Romanovsky wrote:
> Add a new DMA_ATTR_REQUIRE_COHERENT attribute to the DMA API to mark
> mappings that must run on a DMA‑coherent system. Such buffers cannot
> use the SWIOTLB path, may overlap with CPU caches, and do not depend on
> explicit cache flushing.
> 
> Mappings using this attribute are rejected on systems where cache
> side‑effects could lead to data corruption, and therefore do not need
> the cache‑overlap debugging logic. This series also includes fixes for
> DMA_ATTR_CPU_CACHE_CLEAN handling.
> Thanks.

<...>

> ---
> Leon Romanovsky (8):
>       dma-debug: Allow multiple invocations of overlapping entries
>       dma-mapping: handle DMA_ATTR_CPU_CACHE_CLEAN in trace output
>       dma-mapping: Clarify valid conditions for CPU cache line overlap
>       dma-mapping: Introduce DMA require coherency attribute
>       dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set
>       iommu/dma: add support for DMA_ATTR_REQUIRE_COHERENT attribute
>       RDMA/umem: Tell DMA mapping that UMEM requires coherency
>       mm/hmm: Indicate that HMM requires DMA coherency
> 
>  Documentation/core-api/dma-attributes.rst | 38 ++++++++++++++++++++++++-------
>  drivers/infiniband/core/umem.c            |  5 ++--
>  drivers/iommu/dma-iommu.c                 | 21 +++++++++++++----
>  drivers/virtio/virtio_ring.c              | 10 ++++----
>  include/linux/dma-mapping.h               | 15 ++++++++----
>  include/trace/events/dma.h                |  4 +++-
>  kernel/dma/debug.c                        |  9 ++++----
>  kernel/dma/direct.h                       |  7 +++---
>  kernel/dma/mapping.c                      |  6 +++++
>  mm/hmm.c                                  |  4 ++--
>  10 files changed, 86 insertions(+), 33 deletions(-)

Marek,

Despite the "RDMA ..." tag in the subject, the diffstat clearly shows that
you are the appropriate person to take this patch.

Thanks.


> ---
> base-commit: 11439c4635edd669ae435eec308f4ab8a0804808
> change-id: 20260305-dma-debug-overlap-21487c3fa02c
> 
> Best regards,
> --  
> Leon Romanovsky <leonro@nvidia.com>
> 

Re: [PATCH v3 0/8] RDMA: Enable operation with DMA debug enabled

[Marek Szyprowski]

Hi Leon,

On 17.03.2026 20:05, Leon Romanovsky wrote:
> On Mon, Mar 16, 2026 at 09:06:44PM +0200, Leon Romanovsky wrote:
>> Add a new DMA_ATTR_REQUIRE_COHERENT attribute to the DMA API to mark
>> mappings that must run on a DMA‑coherent system. Such buffers cannot
>> use the SWIOTLB path, may overlap with CPU caches, and do not depend on
>> explicit cache flushing.
>>
>> Mappings using this attribute are rejected on systems where cache
>> side‑effects could lead to data corruption, and therefore do not need
>> the cache‑overlap debugging logic. This series also includes fixes for
>> DMA_ATTR_CPU_CACHE_CLEAN handling.
>> Thanks.
> <...>
>
>> ---
>> Leon Romanovsky (8):
>>        dma-debug: Allow multiple invocations of overlapping entries
>>        dma-mapping: handle DMA_ATTR_CPU_CACHE_CLEAN in trace output
>>        dma-mapping: Clarify valid conditions for CPU cache line overlap
>>        dma-mapping: Introduce DMA require coherency attribute
>>        dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set
>>        iommu/dma: add support for DMA_ATTR_REQUIRE_COHERENT attribute
>>        RDMA/umem: Tell DMA mapping that UMEM requires coherency
>>        mm/hmm: Indicate that HMM requires DMA coherency
>>
>>   Documentation/core-api/dma-attributes.rst | 38 ++++++++++++++++++++++++-------
>>   drivers/infiniband/core/umem.c            |  5 ++--
>>   drivers/iommu/dma-iommu.c                 | 21 +++++++++++++----
>>   drivers/virtio/virtio_ring.c              | 10 ++++----
>>   include/linux/dma-mapping.h               | 15 ++++++++----
>>   include/trace/events/dma.h                |  4 +++-
>>   kernel/dma/debug.c                        |  9 ++++----
>>   kernel/dma/direct.h                       |  7 +++---
>>   kernel/dma/mapping.c                      |  6 +++++
>>   mm/hmm.c                                  |  4 ++--
>>   10 files changed, 86 insertions(+), 33 deletions(-)
> Marek,
>
> Despite the "RDMA ..." tag in the subject, the diffstat clearly shows that
> you are the appropriate person to take this patch.

I plan to take the first 2 patches to the dma-mapping-fixes branch 
(v7.0-rc) and the next to dma-mapping-for-next. Should I also take the 
RDMA and HMM patches, or do You want a stable branch for merging them 
via respective subsystem trees?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [PATCH v3 0/8] RDMA: Enable operation with DMA debug enabled

[Leon Romanovsky]

On Wed, Mar 18, 2026 at 09:03:00AM +0100, Marek Szyprowski wrote:
> Hi Leon,
> 
> On 17.03.2026 20:05, Leon Romanovsky wrote:
> > On Mon, Mar 16, 2026 at 09:06:44PM +0200, Leon Romanovsky wrote:
> >> Add a new DMA_ATTR_REQUIRE_COHERENT attribute to the DMA API to mark
> >> mappings that must run on a DMA‑coherent system. Such buffers cannot
> >> use the SWIOTLB path, may overlap with CPU caches, and do not depend on
> >> explicit cache flushing.
> >>
> >> Mappings using this attribute are rejected on systems where cache
> >> side‑effects could lead to data corruption, and therefore do not need
> >> the cache‑overlap debugging logic. This series also includes fixes for
> >> DMA_ATTR_CPU_CACHE_CLEAN handling.
> >> Thanks.
> > <...>
> >
> >> ---
> >> Leon Romanovsky (8):
> >>        dma-debug: Allow multiple invocations of overlapping entries
> >>        dma-mapping: handle DMA_ATTR_CPU_CACHE_CLEAN in trace output
> >>        dma-mapping: Clarify valid conditions for CPU cache line overlap
> >>        dma-mapping: Introduce DMA require coherency attribute
> >>        dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set
> >>        iommu/dma: add support for DMA_ATTR_REQUIRE_COHERENT attribute
> >>        RDMA/umem: Tell DMA mapping that UMEM requires coherency
> >>        mm/hmm: Indicate that HMM requires DMA coherency
> >>
> >>   Documentation/core-api/dma-attributes.rst | 38 ++++++++++++++++++++++++-------
> >>   drivers/infiniband/core/umem.c            |  5 ++--
> >>   drivers/iommu/dma-iommu.c                 | 21 +++++++++++++----
> >>   drivers/virtio/virtio_ring.c              | 10 ++++----
> >>   include/linux/dma-mapping.h               | 15 ++++++++----
> >>   include/trace/events/dma.h                |  4 +++-
> >>   kernel/dma/debug.c                        |  9 ++++----
> >>   kernel/dma/direct.h                       |  7 +++---
> >>   kernel/dma/mapping.c                      |  6 +++++
> >>   mm/hmm.c                                  |  4 ++--
> >>   10 files changed, 86 insertions(+), 33 deletions(-)
> > Marek,
> >
> > Despite the "RDMA ..." tag in the subject, the diffstat clearly shows that
> > you are the appropriate person to take this patch.
> 
> I plan to take the first 2 patches to the dma-mapping-fixes branch 
> (v7.0-rc) and the next to dma-mapping-for-next. Should I also take the 
> RDMA and HMM patches, or do You want a stable branch for merging them 
> via respective subsystem trees?

I suggest taking all patches into the -fixes branch, as the "RDMA/..." patch
also resolves the dmesg splat. With -fixes, there is no need to worry about
a shared branch since we do not expect merge conflicts in that area.

If you still prefer to split the series between -fixes and -next, it would be
better to use a shared branch in that case. There are patches on the RDMA
list targeted for -next that touch ib_umem_get().

Thanks

> 
> Best regards
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
> 
> 

Re: [PATCH v3 0/8] RDMA: Enable operation with DMA debug enabled

[Marek Szyprowski]

Hi Leon,

On 18.03.2026 09:18, Leon Romanovsky wrote:
> On Wed, Mar 18, 2026 at 09:03:00AM +0100, Marek Szyprowski wrote:
>> On 17.03.2026 20:05, Leon Romanovsky wrote:
>>> On Mon, Mar 16, 2026 at 09:06:44PM +0200, Leon Romanovsky wrote:
>>>> Add a new DMA_ATTR_REQUIRE_COHERENT attribute to the DMA API to mark
>>>> mappings that must run on a DMA‑coherent system. Such buffers cannot
>>>> use the SWIOTLB path, may overlap with CPU caches, and do not depend on
>>>> explicit cache flushing.
>>>>
>>>> Mappings using this attribute are rejected on systems where cache
>>>> side‑effects could lead to data corruption, and therefore do not need
>>>> the cache‑overlap debugging logic. This series also includes fixes for
>>>> DMA_ATTR_CPU_CACHE_CLEAN handling.
>>>> Thanks.
>>> <...>
>>>
>>>> ---
>>>> Leon Romanovsky (8):
>>>>         dma-debug: Allow multiple invocations of overlapping entries
>>>>         dma-mapping: handle DMA_ATTR_CPU_CACHE_CLEAN in trace output
>>>>         dma-mapping: Clarify valid conditions for CPU cache line overlap
>>>>         dma-mapping: Introduce DMA require coherency attribute
>>>>         dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set
>>>>         iommu/dma: add support for DMA_ATTR_REQUIRE_COHERENT attribute
>>>>         RDMA/umem: Tell DMA mapping that UMEM requires coherency
>>>>         mm/hmm: Indicate that HMM requires DMA coherency
>>>>
>>>>    Documentation/core-api/dma-attributes.rst | 38 ++++++++++++++++++++++++-------
>>>>    drivers/infiniband/core/umem.c            |  5 ++--
>>>>    drivers/iommu/dma-iommu.c                 | 21 +++++++++++++----
>>>>    drivers/virtio/virtio_ring.c              | 10 ++++----
>>>>    include/linux/dma-mapping.h               | 15 ++++++++----
>>>>    include/trace/events/dma.h                |  4 +++-
>>>>    kernel/dma/debug.c                        |  9 ++++----
>>>>    kernel/dma/direct.h                       |  7 +++---
>>>>    kernel/dma/mapping.c                      |  6 +++++
>>>>    mm/hmm.c                                  |  4 ++--
>>>>    10 files changed, 86 insertions(+), 33 deletions(-)
>>> Marek,
>>>
>>> Despite the "RDMA ..." tag in the subject, the diffstat clearly shows that
>>> you are the appropriate person to take this patch.
>> I plan to take the first 2 patches to the dma-mapping-fixes branch
>> (v7.0-rc) and the next to dma-mapping-for-next. Should I also take the
>> RDMA and HMM patches, or do You want a stable branch for merging them
>> via respective subsystem trees?
> I suggest taking all patches into the -fixes branch, as the "RDMA/..." patch
> also resolves the dmesg splat. With -fixes, there is no need to worry about
> a shared branch since we do not expect merge conflicts in that area.
>
> If you still prefer to split the series between -fixes and -next, it would be
> better to use a shared branch in that case. There are patches on the RDMA
> list targeted for -next that touch ib_umem_get().

Okay, I will merge all patches to the -fixes branch then.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [PATCH v3 0/8] RDMA: Enable operation with DMA debug enabled

[Marek Szyprowski]

On 16.03.2026 20:06, Leon Romanovsky wrote:
> Add a new DMA_ATTR_REQUIRE_COHERENT attribute to the DMA API to mark
> mappings that must run on a DMA‑coherent system. Such buffers cannot
> use the SWIOTLB path, may overlap with CPU caches, and do not depend on
> explicit cache flushing.
>
> Mappings using this attribute are rejected on systems where cache
> side‑effects could lead to data corruption, and therefore do not need
> the cache‑overlap debugging logic. This series also includes fixes for
> DMA_ATTR_CPU_CACHE_CLEAN handling.
> Thanks.
>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

Applied to dma-mapping-fixes. Thanks!

> ---
> Changes in v3:
> - Enriched commit messages and documentation
> - Added ROB tags
> - Link to v2: https://protect2.fireeye.com/v1/url?k=9c1ba148-fd90b40f-9c1a2a07-000babff99aa-86ebd022a97425b3&q=1&e=3c8e10cc-4c34-4bf6-aa9d-c339877d6a27&u=https%3A%2F%2Fpatch.msgid.link%2F20260311-dma-debug-overlap-v2-0-e00bc2ca346d%40nvidia.com
>
> Changes in v2:
> - Added DMA_ATTR_REQUIRE_COHERENT attribute
> - Added HMM patch which needs this attribute as well
> - Renamed DMA_ATTR_CPU_CACHE_CLEAN to be DMA_ATTR_DEBUGGING_IGNORE_CACHELINES
> - Link to v1: https://protect2.fireeye.com/v1/url?k=cc0590de-ad8e8599-cc041b91-000babff99aa-07e4da206b7e0d97&q=1&e=3c8e10cc-4c34-4bf6-aa9d-c339877d6a27&u=https%3A%2F%2Fpatch.msgid.link%2F20260307-dma-debug-overlap-v1-0-c034c38872af%40nvidia.com
>
> ---
> Leon Romanovsky (8):
>        dma-debug: Allow multiple invocations of overlapping entries
>        dma-mapping: handle DMA_ATTR_CPU_CACHE_CLEAN in trace output
>        dma-mapping: Clarify valid conditions for CPU cache line overlap
>        dma-mapping: Introduce DMA require coherency attribute
>        dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set
>        iommu/dma: add support for DMA_ATTR_REQUIRE_COHERENT attribute
>        RDMA/umem: Tell DMA mapping that UMEM requires coherency
>        mm/hmm: Indicate that HMM requires DMA coherency
>
>   Documentation/core-api/dma-attributes.rst | 38 ++++++++++++++++++++++++-------
>   drivers/infiniband/core/umem.c            |  5 ++--
>   drivers/iommu/dma-iommu.c                 | 21 +++++++++++++----
>   drivers/virtio/virtio_ring.c              | 10 ++++----
>   include/linux/dma-mapping.h               | 15 ++++++++----
>   include/trace/events/dma.h                |  4 +++-
>   kernel/dma/debug.c                        |  9 ++++----
>   kernel/dma/direct.h                       |  7 +++---
>   kernel/dma/mapping.c                      |  6 +++++
>   mm/hmm.c                                  |  4 ++--
>   10 files changed, 86 insertions(+), 33 deletions(-)
> ---
> base-commit: 11439c4635edd669ae435eec308f4ab8a0804808
> change-id: 20260305-dma-debug-overlap-21487c3fa02c
>
> Best regards,
> --
> Leon Romanovsky <leonro@nvidia.com>
>
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland