[PATCH v5 0/4] dma-buf: heaps: Turn heaps into modules

[PATCH v5 0/4] dma-buf: heaps: Turn heaps into modules

[Maxime Ripard]

Hi,

The recent introduction of heaps in the optee driver [1] made possible
the creation of heaps as modules.

It's generally a good idea if possible, including for the already
existing system and CMA heaps.

The system one is pretty trivial, the CMA is now easy too with the
reworks we got in 7.1-r1.

Let me know what you think,
Maxime

1: https://lore.kernel.org/dri-devel/20250911135007.1275833-4-jens.wiklander@linaro.org/

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
Changes in v5:
- Rebase on 7.1-rc1
- Add a patch to enable the heaps in arm64 defconfig
- Link to v4: https://lore.kernel.org/r/20260331-dma-buf-heaps-as-modules-v4-0-e18fda504419@kernel.org

Changes in v4:
- Fix compilation failure
- Rework to take into account OF_RESERVED_MEM
- Fix regression making the default CMA area disappear if not created
  through the DT
- Added some documentation and comments
- Link to v3: https://lore.kernel.org/r/20260303-dma-buf-heaps-as-modules-v3-0-24344812c707@kernel.org

Changes in v3:
- Squashed cma_get_name and cma_alloc/release patches
- Fixed typo in Export dev_get_cma_area commit title
- Fixed compilation failure with DMA_CMA but not OF_RESERVED_MEM
- Link to v2: https://lore.kernel.org/r/20260227-dma-buf-heaps-as-modules-v2-0-454aee7e06cc@kernel.org

Changes in v2:
- Collect tags
- Don't export dma_contiguous_default_area anymore, but export
  dev_get_cma_area instead
- Mentioned that heap modules can't be removed
- Link to v1: https://lore.kernel.org/r/20260225-dma-buf-heaps-as-modules-v1-0-2109225a090d@kernel.org

---
Maxime Ripard (4):
      dma-buf: heaps: Export mem_accounting parameter
      dma-buf: heaps: cma: Turn the heap into a module
      dma-buf: heaps: system: Turn the heap into a module
      arm64: defconfig: Enable dma-buf heaps

 arch/arm64/configs/defconfig        | 3 +++
 drivers/dma-buf/dma-heap.c          | 1 +
 drivers/dma-buf/heaps/Kconfig       | 4 ++--
 drivers/dma-buf/heaps/cma_heap.c    | 3 +++
 drivers/dma-buf/heaps/system_heap.c | 5 +++++
 5 files changed, 14 insertions(+), 2 deletions(-)
---
base-commit: 5e9b7d093f3f77cb0af4409559e3d139babfb443
change-id: 20260225-dma-buf-heaps-as-modules-1034b3ec9f2a

Best regards,
-- 
Maxime Ripard <mripard@kernel.org>

[PATCH v5 1/4] dma-buf: heaps: Export mem_accounting parameter

[Maxime Ripard]

The mem_accounting kernel parameter is used by heaps to know if they
should account allocations in their respective cgroup controllers.

Since we're going to allow heaps to compile as modules, we need to
export that variable.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/dma-buf/dma-heap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index ac5f8685a649..a76bf3f8b071 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -51,10 +51,11 @@ static DEFINE_XARRAY_ALLOC(dma_heap_minors);
 
 bool __read_mostly mem_accounting;
 module_param(mem_accounting, bool, 0444);
 MODULE_PARM_DESC(mem_accounting,
 		 "Enable cgroup-based memory accounting for dma-buf heap allocations (default=false).");
+EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP");
 
 static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
 				 u32 fd_flags,
 				 u64 heap_flags)
 {

-- 
2.53.0

Claude review: dma-buf: heaps: Export mem_accounting parameter

[Claude Code Review Bot]

Patch Review

**Change:** Adds `EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP")` after the existing `module_param` declaration in `drivers/dma-buf/dma-heap.c`.

This is correct and necessary. The `mem_accounting` variable is declared `extern` in `include/linux/dma-heap.h:49` and is used by `system_heap.c:388`. Without this export, building `system_heap.c` as a module would fail at link time. Using `_NS_GPL` with the `"DMA_BUF_HEAP"` namespace is consistent with the existing export namespace for the dma-buf heap APIs.

Note that `cma_heap.c` does not currently reference `mem_accounting`, so this export is strictly needed only for the system heap (patch 3), not the CMA heap (patch 2). The ordering is still correct since patch 1 logically prepares the infrastructure for both module conversions.

No issues.

---
Generated by Claude Code Patch Reviewer

[PATCH v5 2/4] dma-buf: heaps: cma: Turn the heap into a module

[Maxime Ripard]

All the symbols used by the CMA heap are already exported, so turning it
into a module is straightforward. We only need to add the usual MODULE_*
macros, import the proper namespaces and change the Kconfig symbol to a
tristate.

This heap won't be able to unload though, since we're missing a lot of
infrastructure to make it safe.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/dma-buf/heaps/Kconfig    | 2 +-
 drivers/dma-buf/heaps/cma_heap.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig
index a5eef06c4226..aed0b9b4febf 100644
--- a/drivers/dma-buf/heaps/Kconfig
+++ b/drivers/dma-buf/heaps/Kconfig
@@ -4,11 +4,11 @@ config DMABUF_HEAPS_SYSTEM
 	help
 	  Choose this option to enable the system dmabuf heap. The system heap
 	  is backed by pages from the buddy allocator. If in doubt, say Y.
 
 config DMABUF_HEAPS_CMA
-	bool "DMA-BUF CMA Heap"
+	tristate "DMA-BUF CMA Heap"
 	depends on DMABUF_HEAPS && DMA_CMA
 	help
 	  Choose this option to enable dma-buf CMA heap. This heap is backed
 	  by the Contiguous Memory Allocator (CMA). If your system has these
 	  regions, you should say Y here.
diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
index a359aac45579..3fb4b946c91a 100644
--- a/drivers/dma-buf/heaps/cma_heap.c
+++ b/drivers/dma-buf/heaps/cma_heap.c
@@ -418,5 +418,8 @@ static int __init add_cma_heaps(void)
 
 	return 0;
 }
 module_init(add_cma_heaps);
 MODULE_DESCRIPTION("DMA-BUF CMA Heap");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("DMA_BUF");
+MODULE_IMPORT_NS("DMA_BUF_HEAP");

-- 
2.53.0

Claude review: dma-buf: heaps: cma: Turn the heap into a module

[Claude Code Review Bot]

Patch Review

**Change:** 
- `drivers/dma-buf/heaps/Kconfig`: `DMABUF_HEAPS_CMA` changed from `bool` to `tristate`
- `drivers/dma-buf/heaps/cma_heap.c`: Adds `MODULE_LICENSE("GPL")`, `MODULE_IMPORT_NS("DMA_BUF")`, `MODULE_IMPORT_NS("DMA_BUF_HEAP")`

The commit message correctly notes this heap can't be unloaded since there is no `module_exit` function — confirmed by grep showing no `module_exit` in any heap source. This is a deliberate design choice; the kernel will simply refuse to unload the module. The cover letter and v2 changelog mention this was documented.

The two `MODULE_IMPORT_NS` lines match the namespaces used by `dma_heap_add()` (exported in `"DMA_BUF"`) and `mem_accounting` (exported in `"DMA_BUF_HEAP"`). Even though `cma_heap.c` doesn't directly use `mem_accounting`, importing `DMA_BUF_HEAP` is fine as the CMA heap uses other `DMA_BUF_HEAP`-namespaced symbols.

No issues.

---
Generated by Claude Code Patch Reviewer

[PATCH v5 3/4] dma-buf: heaps: system: Turn the heap into a module

[Maxime Ripard]

The system heap can be easily turned into a module by adding the usual
MODULE_* macros, importing the proper namespaces and changing the
Kconfig symbol to a tristate.

This heap won't be able to unload though, since we're missing a lot of
infrastructure to make it safe.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/dma-buf/heaps/Kconfig       | 2 +-
 drivers/dma-buf/heaps/system_heap.c | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig
index aed0b9b4febf..e273fb18feca 100644
--- a/drivers/dma-buf/heaps/Kconfig
+++ b/drivers/dma-buf/heaps/Kconfig
@@ -1,7 +1,7 @@
 config DMABUF_HEAPS_SYSTEM
-	bool "DMA-BUF System Heap"
+	tristate "DMA-BUF System Heap"
 	depends on DMABUF_HEAPS
 	help
 	  Choose this option to enable the system dmabuf heap. The system heap
 	  is backed by pages from the buddy allocator. If in doubt, say Y.
 
diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 03c2b87cb111..c92bdec356fc 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -535,5 +535,10 @@ static int __init system_heap_create(void)
 		return PTR_ERR(sys_heap);
 
 	return 0;
 }
 module_init(system_heap_create);
+
+MODULE_DESCRIPTION("DMA-BUF System Heap");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("DMA_BUF");
+MODULE_IMPORT_NS("DMA_BUF_HEAP");

-- 
2.53.0

Claude review: dma-buf: heaps: system: Turn the heap into a module

[Claude Code Review Bot]

Patch Review

**Change:**
- `drivers/dma-buf/heaps/Kconfig`: `DMABUF_HEAPS_SYSTEM` changed from `bool` to `tristate`
- `drivers/dma-buf/heaps/system_heap.c`: Adds `MODULE_DESCRIPTION("DMA-BUF System Heap")`, `MODULE_LICENSE("GPL")`, `MODULE_IMPORT_NS("DMA_BUF")`, `MODULE_IMPORT_NS("DMA_BUF_HEAP")`

Same pattern as the CMA heap patch. This one also adds `MODULE_DESCRIPTION` which the CMA heap already had from a prior commit. The namespace imports are correct — this heap directly uses `mem_accounting` (at line 388), so the `DMA_BUF_HEAP` import is needed.

Same no-`module_exit` situation applies here, correctly documented.

No issues.

---
Generated by Claude Code Patch Reviewer

[PATCH v5 4/4] arm64: defconfig: Enable dma-buf heaps

[Maxime Ripard]

Now that the system and CMA heaps can be built as modules, enable both
as modules in the arm64 defconfig.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 arch/arm64/configs/defconfig | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
index d905a0777f93..f33193b50e6b 100644
--- a/arch/arm64/configs/defconfig
+++ b/arch/arm64/configs/defconfig
@@ -1409,10 +1409,13 @@ CONFIG_RCAR_DMAC=y
 CONFIG_RENESAS_USB_DMAC=m
 CONFIG_RZ_DMAC=y
 CONFIG_TI_K3_UDMA=y
 CONFIG_TI_K3_UDMA_GLUE_LAYER=y
 CONFIG_STM32_DMA3=m
+CONFIG_DMABUF_HEAPS=y
+CONFIG_DMABUF_HEAPS_SYSTEM=m
+CONFIG_DMABUF_HEAPS_CMA=m
 CONFIG_VFIO=y
 CONFIG_VFIO_PCI=y
 CONFIG_VIRTIO_PCI=y
 CONFIG_VIRTIO_BALLOON=y
 CONFIG_VIRTIO_MMIO=y

-- 
2.53.0

Claude review: arm64: defconfig: Enable dma-buf heaps

[Claude Code Review Bot]

Patch Review

**Change:** Adds three lines to `arch/arm64/configs/defconfig`:
```
CONFIG_DMABUF_HEAPS=y
CONFIG_DMABUF_HEAPS_SYSTEM=m
CONFIG_DMABUF_HEAPS_CMA=m
```

The placement is between `CONFIG_STM32_DMA3=m` and `CONFIG_VFIO=y` (confirmed at lines 1413-1417 in the applied tree). The base framework (`DMABUF_HEAPS`) is `=y` which is required since the heaps depend on it and it's a `bool`. Both heaps are `=m` which exercises the new tristate functionality.

**Minor observation:** The defconfig insertion point is in the DMA engine section (between STM32_DMA3 and VFIO). This is arguably fine since defconfigs aren't strictly section-organized by subsystem, but one could argue these belong near other dmabuf/graphics config entries. This is purely cosmetic and not worth blocking on.

No issues.

---
Generated by Claude Code Patch Reviewer

Claude review: dma-buf: heaps: Turn heaps into modules

[Claude Code Review Bot]

Overall Series Review

Subject: dma-buf: heaps: Turn heaps into modules
Author: Maxime Ripard <mripard@kernel.org>
Patches: 5
Reviewed: 2026-04-28T14:45:00.914337

---

This is a clean, well-scoped 4-patch series from Maxime Ripard that converts the DMA-BUF CMA and system heaps from `bool` Kconfig options to `tristate`, allowing them to be built as loadable modules. The series is straightforward: patch 1 exports the one remaining unexported symbol (`mem_accounting`), patches 2-3 add the MODULE_* macros and change the Kconfig type for each heap, and patch 4 enables both as `=m` in the arm64 defconfig.

The series is at v5 and already carries `Reviewed-by: T.J. Mercier` on patches 1-3. The changes are minimal, correct, and well-ordered. No significant issues found.

**Verdict: Looks good to merge.**

One minor observation below, but nothing blocking.

---

---
Generated by Claude Code Patch Reviewer

[PATCH v4 0/8] dma-buf: heaps: Turn heaps into modules

[Maxime Ripard]

Hi,

The recent introduction of heaps in the optee driver [1] made possible
the creation of heaps as modules.

It's generally a good idea if possible, including for the already
existing system and CMA heaps.

The system one is pretty trivial, the CMA one is a bit more involved,
especially since we have a call from kernel/dma/contiguous.c to the CMA
heap code. This was solved by turning the logic around and making the
CMA heap call into the contiguous DMA code.

Let me know what you think,
Maxime

1: https://lore.kernel.org/dri-devel/20250911135007.1275833-4-jens.wiklander@linaro.org/

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
Changes in v4:
- Fix compilation failure
- Rework to take into account OF_RESERVED_MEM
- Fix regression making the default CMA area disappear if not created
  through the DT
- Added some documentation and comments
- Link to v3: https://lore.kernel.org/r/20260303-dma-buf-heaps-as-modules-v3-0-24344812c707@kernel.org

Changes in v3:
- Squashed cma_get_name and cma_alloc/release patches
- Fixed typo in Export dev_get_cma_area commit title
- Fixed compilation failure with DMA_CMA but not OF_RESERVED_MEM
- Link to v2: https://lore.kernel.org/r/20260227-dma-buf-heaps-as-modules-v2-0-454aee7e06cc@kernel.org

Changes in v2:
- Collect tags
- Don't export dma_contiguous_default_area anymore, but export
  dev_get_cma_area instead
- Mentioned that heap modules can't be removed
- Link to v1: https://lore.kernel.org/r/20260225-dma-buf-heaps-as-modules-v1-0-2109225a090d@kernel.org

---
Maxime Ripard (8):
      dma: contiguous: Turn heap registration logic around
      dma: contiguous: Make dev_get_cma_area() a proper function
      dma: contiguous: Make dma_contiguous_default_area static
      dma: contiguous: Export dev_get_cma_area()
      mm: cma: Export cma_alloc(), cma_release() and cma_get_name()
      dma-buf: heaps: Export mem_accounting parameter
      dma-buf: heaps: cma: Turn the heap into a module
      dma-buf: heaps: system: Turn the heap into a module

 drivers/dma-buf/dma-heap.c          |  1 +
 drivers/dma-buf/heaps/Kconfig       |  4 +--
 drivers/dma-buf/heaps/cma_heap.c    | 22 +++----------
 drivers/dma-buf/heaps/system_heap.c |  5 +++
 include/linux/dma-buf/heaps/cma.h   | 16 ---------
 include/linux/dma-map-ops.h         | 14 ++++----
 kernel/dma/contiguous.c             | 66 +++++++++++++++++++++++++++++++++----
 mm/cma.c                            |  3 ++
 8 files changed, 82 insertions(+), 49 deletions(-)
---
base-commit: c081b71f11732ad2c443f170ab19c3ebe8a1a422
change-id: 20260225-dma-buf-heaps-as-modules-1034b3ec9f2a

Best regards,
-- 
Maxime Ripard <mripard@kernel.org>

[PATCH v4 6/8] dma-buf: heaps: Export mem_accounting parameter

[Maxime Ripard]

The mem_accounting kernel parameter is used by heaps to know if they
should account allocations in their respective cgroup controllers.

Since we're going to allow heaps to compile as modules, we need to
export that variable.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/dma-buf/dma-heap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index ac5f8685a649496c0e1c6decbf263b63fa472d04..a76bf3f8b071a3d5bf39a8513f31e9e8aa16e02f 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -51,10 +51,11 @@ static DEFINE_XARRAY_ALLOC(dma_heap_minors);
 
 bool __read_mostly mem_accounting;
 module_param(mem_accounting, bool, 0444);
 MODULE_PARM_DESC(mem_accounting,
 		 "Enable cgroup-based memory accounting for dma-buf heap allocations (default=false).");
+EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP");
 
 static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
 				 u32 fd_flags,
 				 u64 heap_flags)
 {

-- 
2.53.0

Claude review: dma-buf: heaps: Export mem_accounting parameter

[Claude Code Review Bot]

Patch Review

```c
EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP");
```

Uses namespaced export (`DMA_BUF_HEAP`), which is good practice to limit visibility. The heaps in patches 7 and 8 import this namespace.

No issues.

---
Generated by Claude Code Patch Reviewer

[PATCH v3 0/8] dma-buf: heaps: Turn heaps into modules

[Maxime Ripard]

Hi,

The recent introduction of heaps in the optee driver [1] made possible
the creation of heaps as modules.

It's generally a good idea if possible, including for the already
existing system and CMA heaps.

The system one is pretty trivial, the CMA one is a bit more involved,
especially since we have a call from kernel/dma/contiguous.c to the CMA
heap code. This was solved by turning the logic around and making the
CMA heap call into the contiguous DMA code.

Let me know what you think,
Maxime

1: https://lore.kernel.org/dri-devel/20250911135007.1275833-4-jens.wiklander@linaro.org/

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
Changes in v3:
- Squashed cma_get_name and cma_alloc/release patches
- Fixed typo in Export dev_get_cma_area commit title
- Fixed compilation failure with DMA_CMA but not OF_RESERVED_MEM
- Link to v2: https://lore.kernel.org/r/20260227-dma-buf-heaps-as-modules-v2-0-454aee7e06cc@kernel.org

Changes in v2:
- Collect tags
- Don't export dma_contiguous_default_area anymore, but export
  dev_get_cma_area instead
- Mentioned that heap modules can't be removed
- Link to v1: https://lore.kernel.org/r/20260225-dma-buf-heaps-as-modules-v1-0-2109225a090d@kernel.org

---
Maxime Ripard (8):
      dma: contiguous: Turn heap registration logic around
      dma: contiguous: Make dev_get_cma_area() a proper function
      dma: contiguous: Make dma_contiguous_default_area static
      dma: contiguous: Export dev_get_cma_area()
      mm: cma: Export cma_alloc(), cma_release() and cma_get_name()
      dma-buf: heaps: Export mem_accounting parameter
      dma-buf: heaps: cma: Turn the heap into a module
      dma-buf: heaps: system: Turn the heap into a module

 drivers/dma-buf/dma-heap.c          |  1 +
 drivers/dma-buf/heaps/Kconfig       |  4 ++--
 drivers/dma-buf/heaps/cma_heap.c    | 21 +++++----------------
 drivers/dma-buf/heaps/system_heap.c |  5 +++++
 include/linux/dma-map-ops.h         | 18 ++++++++++--------
 kernel/dma/contiguous.c             | 37 ++++++++++++++++++++++++++++++++++---
 mm/cma.c                            |  3 +++
 7 files changed, 60 insertions(+), 29 deletions(-)
---
base-commit: 499a718536dc0e1c1d1b6211847207d58acd9916
change-id: 20260225-dma-buf-heaps-as-modules-1034b3ec9f2a

Best regards,
-- 
Maxime Ripard <mripard@kernel.org>

[PATCH v3 6/8] dma-buf: heaps: Export mem_accounting parameter

[Maxime Ripard]

The mem_accounting kernel parameter is used by heaps to know if they
should account allocations in their respective cgroup controllers.

Since we're going to allow heaps to compile as modules, we need to
export that variable.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/dma-buf/dma-heap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index ac5f8685a649496c0e1c6decbf263b63fa472d04..a76bf3f8b071a3d5bf39a8513f31e9e8aa16e02f 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -51,10 +51,11 @@ static DEFINE_XARRAY_ALLOC(dma_heap_minors);
 
 bool __read_mostly mem_accounting;
 module_param(mem_accounting, bool, 0444);
 MODULE_PARM_DESC(mem_accounting,
 		 "Enable cgroup-based memory accounting for dma-buf heap allocations (default=false).");
+EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP");
 
 static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
 				 u32 fd_flags,
 				 u64 heap_flags)
 {

-- 
2.53.0

Claude review: dma-buf: heaps: Export mem_accounting parameter

[Claude Code Review Bot]

Patch Review

Exports the `mem_accounting` module parameter using `EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP")`. The use of the `DMA_BUF_HEAP` namespace is consistent with how `dma_heap_add` is already exported (confirmed at `dma-heap.c:315`).

No issues.

---
Generated by Claude Code Patch Reviewer

[PATCH 0/7] dma-buf: heaps: Turn heaps into modules

[Maxime Ripard]

Hi,

The recent introduction of heaps in the optee driver [1] made possible
the creation of heaps as modules.

It's generally a good idea if possible, including for the already
existing system and CMA heaps.

The system one is pretty trivial, the CMA one is a bit more involved,
especially since we have a call from kernel/dma/contiguous.c to the CMA
heap code. This was solved by turning the logic around and making the
CMA heap call into the contiguous DMA code.

Let me know what you think,
Maxime

1: https://lore.kernel.org/dri-devel/20250911135007.1275833-4-jens.wiklander@linaro.org/

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
Maxime Ripard (7):
      dma: contiguous: Turn heap registration logic around
      mm: cma: Export cma_alloc and cma_release
      mm: cma: Export cma_get_name
      mm: cma: Export dma_contiguous_default_area
      dma-buf: heaps: Export mem_accounting parameter
      dma-buf: heaps: cma: Turn the heap into a module
      dma-buf: heaps: system: Turn the heap into a module

 drivers/dma-buf/dma-heap.c          |  1 +
 drivers/dma-buf/heaps/Kconfig       |  4 ++--
 drivers/dma-buf/heaps/cma_heap.c    | 21 +++++----------------
 drivers/dma-buf/heaps/system_heap.c |  5 +++++
 include/linux/dma-map-ops.h         |  5 +++++
 kernel/dma/contiguous.c             | 27 +++++++++++++++++++++++++--
 mm/cma.c                            |  3 +++
 7 files changed, 46 insertions(+), 20 deletions(-)
---
base-commit: 499a718536dc0e1c1d1b6211847207d58acd9916
change-id: 20260225-dma-buf-heaps-as-modules-1034b3ec9f2a

Best regards,
-- 
Maxime Ripard <mripard@kernel.org>

[PATCH 5/7] dma-buf: heaps: Export mem_accounting parameter

[Maxime Ripard]

The mem_accounting kernel parameter is used by heaps to know if they
should account allocations in their respective cgroup controllers.

Since we're going to allow heaps to compile as modules, we need to
export that variable.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/dma-buf/dma-heap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index ac5f8685a649496c0e1c6decbf263b63fa472d04..a76bf3f8b071a3d5bf39a8513f31e9e8aa16e02f 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -51,10 +51,11 @@ static DEFINE_XARRAY_ALLOC(dma_heap_minors);
 
 bool __read_mostly mem_accounting;
 module_param(mem_accounting, bool, 0444);
 MODULE_PARM_DESC(mem_accounting,
 		 "Enable cgroup-based memory accounting for dma-buf heap allocations (default=false).");
+EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP");
 
 static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
 				 u32 fd_flags,
 				 u64 heap_flags)
 {

-- 
2.53.0

Claude review: dma-buf: heaps: Export mem_accounting parameter

[Claude Code Review Bot]

Patch Review

```c
+EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP");
```

**Observation:** The `DMA_BUF_HEAP` namespace is correct and matches the namespace used by `dma_heap_add()`, `dma_heap_get_drvdata()`, etc. However, `mem_accounting` is currently only used by `system_heap.c` (not `cma_heap.c`). The CMA heap imports this namespace in patch 6 anyway (for `dma_heap_add`), so this is harmless, but worth noting that `mem_accounting` isn't actually consumed by the CMA heap.

---
Generated by Claude Code Patch Reviewer