linux.git/kernel/dma/contiguous.c, branch v6.18.21

of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

2026-02-06T15:57:35+00:00

[ Upstream commit 0fd17e5983337231dc655e9ca0095d2ca3f47405 ]

When initializing the default cma region, the "cma=" kernel parameter
takes priority over a DT defined linux,cma-default region. Hence, give
the reserved_mem framework the ability to detect this so that the DT
defined cma region can skip initialization accordingly.

Signed-off-by: Oreoluwa Babatunde 
Tested-by: Joy Zou 
Acked-by: Rob Herring (Arm) 
Fixes: 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved memory regions are processed")
Fixes: 2c223f7239f3 ("of: reserved_mem: Restructure call site for dma_contiguous_early_fixup()")
Link: https://lore.kernel.org/r/20251210002027.1171519-1-oreoluwa.babatunde@oss.qualcomm.com
[mszyprow: rebased onto v6.19-rc1, added fixes tags, added a stub for
 cma_skip_dt_default_reserved_mem() if no CONFIG_DMA_CMA is set]
Signed-off-by: Marek Szyprowski 
Signed-off-by: Sasha Levin

of: reserved_mem: Restructure call site for dma_contiguous_early_fixup()

2025-08-11T11:05:38+00:00

Restructure the call site for dma_contiguous_early_fixup() to
where the reserved_mem nodes are being parsed from the DT so that
dma_mmu_remap[] is populated before dma_contiguous_remap() is called.

Fixes: 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved memory regions are processed")
Signed-off-by: Oreoluwa Babatunde 
Tested-by: William Zhang 
Signed-off-by: Marek Szyprowski 
Link: https://lore.kernel.org/r/20250806172421.2748302-1-oreoluwa.babatunde@oss.qualcomm.com

dma-contiguous: hornor the cma address limit setup by user

2025-06-12T06:38:40+00:00

When porting a cma related usage from x86_64 server to arm64 server,
the "cma=4G@4G" setup failed on arm64. The reason is arm64 and some
other architectures have specific physical address limit for reserved
cma area, like 4GB due to the device's need for 32 bit dma. Actually
lots of platforms of those architectures don't have this device dma
limit, but still have to obey it, and are not able to reserve a huge
cma pool.

This situation could be improved by honoring the user input cma
physical address than the arch limit. As when users specify it, they
already knows what the default is which probably can't suit them.

Suggested-by: Robin Murphy 
Signed-off-by: Feng Tang 
Signed-off-by: Marek Szyprowski 
Link: https://lore.kernel.org/r/20250612021417.44929-1-feng.tang@linux.alibaba.com

dma/contiguous: avoid warning about unused size_bytes

2025-04-09T15:28:53+00:00

When building with W=1, this variable is unused for configs with
CONFIG_CMA_SIZE_SEL_PERCENTAGE=y:

kernel/dma/contiguous.c:67:26: error: 'size_bytes' defined but not used [-Werror=unused-const-variable=]

Change this to a macro to avoid the warning.

Fixes: c64be2bb1c6e ("drivers: add Contiguous Memory Allocator")
Signed-off-by: Arnd Bergmann 
Signed-off-by: Marek Szyprowski 
Link: https://lore.kernel.org/r/20250409151557.3890443-1-arnd@kernel.org

mm/cma: drop CONFIG_CMA_DEBUG

2024-02-22T18:24:53+00:00

All pr_debug() prints in (mm/cma.c) could be enabled via standard Makefile
based method.  Besides cma_debug_show_areas() should always be called
during cma_alloc() failure path.  This seemingly redundant config,
CONFIG_CMA_DEBUG can be dropped without any problem.

[lukas.bulwahn@gmail.com: remove debug code to removed CONFIG_CMA_DEBUG]
  Link: https://lkml.kernel.org/r/20240207143825.986-1-lukas.bulwahn@gmail.com
Link: https://lkml.kernel.org/r/20240205031647.283510-1-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual 
Signed-off-by: Lukas Bulwahn 
Cc: Christoph Hellwig 
Cc: Marek Szyprowski 
Cc: Robin Murphy 
Signed-off-by: Andrew Morton

Revert "dma-contiguous: check for memory region overlap"

2023-09-08T08:58:32+00:00

This reverts commit 3fa6456ebe13adab3ba1817c8e515a5b88f95dce.

The Commit broke the CMA region creation through DT on arm64,
as showed below logs with "memblock=debug":
[    0.000000] memblock_phys_alloc_range: 41943040 bytes align=0x200000
from=0x0000000000000000 max_addr=0x00000000ffffffff
early_init_dt_alloc_reserved_memory_arch+0x34/0xa0
[    0.000000] memblock_reserve: [0x00000000fd600000-0x00000000ffdfffff]
memblock_alloc_range_nid+0xc0/0x19c
[    0.000000] Reserved memory: overlap with other memblock reserved region

>From call flow, region we defined in DT was always reserved before entering
into rmem_cma_setup. Also, rmem_cma_setup has one routine cma_init_reserved_mem
to ensure the region was reserved. Checking the region not reserved here seems
not correct.

early_init_fdt_scan_reserved_mem:
    fdt_scan_reserved_mem
        __reserved_mem_reserve_reg
		early_init_dt_reserve_memory
			memblock_reserve(using “reg” prop case)
        fdt_init_reserved_mem
		__reserved_mem_alloc_size
			*early_init_dt_alloc_reserved_memory_arch*
				memblock_reserve(dynamic alloc case)
        __reserved_mem_init_node
		rmem_cma_setup(region overlap check here should always fail)

Example DT can be used to reproduce issue:

    dump_mem: mem_dump_region {
            compatible = "shared-dma-pool";
            alloc-ranges = <0x0 0x00000000 0x0 0xffffffff>;
            reusable;
            size = <0 0x2800000>;
    };

Signed-off-by: Zhenhua Huang

dma-contiguous: check for memory region overlap

2023-07-31T15:54:56+00:00

In the process of parsing the DTS, check whether the memory region
specified by the DTS CMA node area overlaps with the kernel text
memory space reserved by memblock before calling
early_init_fdt_scan_reserved_mem.

Signed-off-by: Binglei Wang 
Signed-off-by: Christoph Hellwig

dma-contiguous: support numa CMA for specified node

2023-07-31T15:54:29+00:00

The kernel parameter 'cma_pernuma=' only supports reserving the same
size of CMA area for each node. We need to reserve different sizes of
CMA area for specified nodes if these devices belong to different nodes.

Adding another kernel parameter 'numa_cma=' to reserve CMA area for
the specified node. If we want to use one of these parameters, we need to
enable DMA_NUMA_CMA.

At the same time, print the node id in cma_declare_contiguous_nid() if
CONFIG_NUMA is enabled.

Signed-off-by: Yajun Deng 
Signed-off-by: Christoph Hellwig

dma-contiguous: support per-numa CMA for all architectures

2023-07-31T15:54:28+00:00

In the commit b7176c261cdb ("dma-contiguous: provide the ability to
reserve per-numa CMA"), Barry adds DMA_PERNUMA_CMA for ARM64.

But this feature is architecture independent, so support per-numa CMA
for all architectures, and enable it by default if NUMA.

Signed-off-by: Yajun Deng 
Tested-by: Yicong Yang 
Signed-off-by: Christoph Hellwig

cma: factor out minimum alignment requirement

2022-03-22T22:57:05+00:00

Patch series "mm: enforce pageblock_order < MAX_ORDER".

Having pageblock_order >= MAX_ORDER seems to be able to happen in corner
cases and some parts of the kernel are not prepared for it.

For example, Aneesh has shown [1] that such kernels can be compiled on
ppc64 with 64k base pages by setting FORCE_MAX_ZONEORDER=8, which will
run into a WARN_ON_ONCE(order >= MAX_ORDER) in comapction code right
during boot.

We can get pageblock_order >= MAX_ORDER when the default hugetlb size is
bigger than the maximum allocation granularity of the buddy, in which
case we are no longer talking about huge pages but instead gigantic
pages.

Having pageblock_order >= MAX_ORDER can only make alloc_contig_range()
of such gigantic pages more likely to succeed.

Reliable use of gigantic pages either requires boot time allcoation or
CMA, no need to overcomplicate some places in the kernel to optimize for
corner cases that are broken in other areas of the kernel.

This patch (of 2):

Let's enforce pageblock_order < MAX_ORDER and simplify.

Especially patch #1 can be regarded a cleanup before:
	[PATCH v5 0/6] Use pageblock_order for cma and alloc_contig_range
	alignment. [2]

[1] https://lkml.kernel.org/r/87r189a2ks.fsf@linux.ibm.com
[2] https://lkml.kernel.org/r/20220211164135.1803616-1-zi.yan@sent.com

Link: https://lkml.kernel.org/r/20220214174132.219303-2-david@redhat.com
Signed-off-by: David Hildenbrand 
Reviewed-by: Zi Yan 
Acked-by: Rob Herring 
Cc: Aneesh Kumar K.V 
Cc: Michael Ellerman 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Frank Rowand 
Cc: Michael S. Tsirkin 
Cc: Christoph Hellwig 
Cc: Marek Szyprowski 
Cc: Robin Murphy 
Cc: Minchan Kim 
Cc: Vlastimil Babka 
Cc: John Garry via iommu 

Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds