Message-ID: <20250226115044.zw44p5dxlhy5eoni@pengutronix.de>
Date: Wed, 26 Feb 2025 12:50:44 +0100
From: Marco Felsch <m.felsch@...gutronix.de>
To: Oreoluwa Babatunde <quic_obabatun@...cinc.com>
Cc: robh@...nel.org, aisheng.dong@....com, andy@...ck.fi.intel.com,
	catalin.marinas@....com, devicetree@...r.kernel.org, hch@....de,
	iommu@...ts.linux.dev, kernel@...cinc.com, klarasmodin@...il.com,
	linux-kernel@...r.kernel.org, m.szyprowski@...sung.com,
	quic_ninanaik@...cinc.com, robin.murphy@....com,
	saravanak@...gle.com, will@...nel.org, stable@...r.kernel.org,
	kernel@...gutronix.de, sashal@...nel.org
Subject: Re: [PATCH v10 1/2] of: reserved_mem: Restruture how the reserved
 memory regions are processed

Hi,

On 24-10-08, Oreoluwa Babatunde wrote:
> Reserved memory regions defined in the devicetree can be broken up into
> two groups:
> i) Statically-placed reserved memory regions
> i.e. regions defined with a static start address and size using the
>      "reg" property.
> ii) Dynamically-placed reserved memory regions.
> i.e. regions defined by specifying an address range where they can be
>      placed in memory using the "alloc_ranges" and "size" properties.
> 
> These regions are processed and set aside at boot time.
> This is done in two stages as seen below:
> 
> Stage 1:
> At this stage, fdt_scan_reserved_mem() scans through the child nodes of
> the reserved_memory node using the flattened devicetree and does the
> following:
> 
> 1) If the node represents a statically-placed reserved memory region,
>    i.e. if it is defined using the "reg" property:
>    - Call memblock_reserve() or memblock_mark_nomap() as needed.
>    - Add the information for that region into the reserved_mem array
>      using fdt_reserved_mem_save_node().
>      i.e. fdt_reserved_mem_save_node(node, name, base, size).
> 
> 2) If the node represents a dynamically-placed reserved memory region,
>    i.e. if it is defined using "alloc-ranges" and "size" properties:
>    - Add the information for that region to the reserved_mem array with
>      the starting address and size set to 0.
>      i.e. fdt_reserved_mem_save_node(node, name, 0, 0).
>    Note: This region is saved to the array with a starting address of 0
>    because a starting address is not yet allocated for it.
> 
> Stage 2:
> After iterating through all the reserved memory nodes and storing their
> relevant information in the reserved_mem array,fdt_init_reserved_mem() is
> called and does the following:
> 
> 1) For statically-placed reserved memory regions:
>    - Call the region specific init function using
>      __reserved_mem_init_node().
> 2) For dynamically-placed reserved memory regions:
>    - Call __reserved_mem_alloc_size() which is used to allocate memory
>      for each of these regions, and mark them as nomap if they have the
>      nomap property specified in the DT.
>    - Call the region specific init function.
> 
> The current size of the resvered_mem array is 64 as is defined by
> MAX_RESERVED_REGIONS. This means that there is a limitation of 64 for
> how many reserved memory regions can be specified on a system.
> As systems continue to grow more and more complex, the number of
> reserved memory regions needed are also growing and are starting to hit
> this 64 count limit, hence the need to make the reserved_mem array
> dynamically sized (i.e. dynamically allocating memory for the
> reserved_mem array using membock_alloc_*).
> 
> On architectures such as arm64, memory allocated using memblock is
> writable only after the page tables have been setup. This means that if
> the reserved_mem array is going to be dynamically allocated, it needs to
> happen after the page tables have been setup, not before.
> 
> Since the reserved memory regions are currently being processed and
> added to the array before the page tables are setup, there is a need to
> change the order in which some of the processing is done to allow for
> the reserved_mem array to be dynamically sized.
> 
> It is possible to process the statically-placed reserved memory regions
> without needing to store them in the reserved_mem array until after the
> page tables have been setup because all the information stored in the
> array is readily available in the devicetree and can be referenced at
> any time.
> Dynamically-placed reserved memory regions on the other hand get
> assigned a start address only at runtime, and hence need a place to be
> stored once they are allocated since there is no other referrence to the
> start address for these regions.
> 
> Hence this patch changes the processing order of the reserved memory
> regions in the following ways:
> 
> Step 1:
> fdt_scan_reserved_mem() scans through the child nodes of
> the reserved_memory node using the flattened devicetree and does the
> following:
> 
> 1) If the node represents a statically-placed reserved memory region,
>    i.e. if it is defined using the "reg" property:
>    - Call memblock_reserve() or memblock_mark_nomap() as needed.
> 
> 2) If the node represents a dynamically-placed reserved memory region,
>    i.e. if it is defined using "alloc-ranges" and "size" properties:
>    - Call __reserved_mem_alloc_size() which will:
>      i) Allocate memory for the reserved region and call
>      memblock_mark_nomap() as needed.
>      ii) Call the region specific initialization function using
>      fdt_init_reserved_mem_node().
>      iii) Save the region information in the reserved_mem array using
>      fdt_reserved_mem_save_node().
> 
> Step 2:
> 1) This stage of the reserved memory processing is now only used to add
>    the statically-placed reserved memory regions into the reserved_mem
>    array using fdt_scan_reserved_mem_reg_nodes(), as well as call their
>    region specific initialization functions.
> 
> 2) This step has also been moved to be after the page tables are
>    setup. Moving this will allow us to replace the reserved_mem
>    array with a dynamically sized array before storing the rest of
>    these regions.
> 
> Signed-off-by: Oreoluwa Babatunde <quic_obabatun@...cinc.com>
> ---
>  drivers/of/fdt.c             |   5 +-
>  drivers/of/of_private.h      |   3 +-
>  drivers/of/of_reserved_mem.c | 168 ++++++++++++++++++++++++-----------
>  3 files changed, 122 insertions(+), 54 deletions(-)

this patch got into stable kernel 6.12.13++ as part of Stable-dep-of.
The stable kernel commit is: 9a0fe62f93ede02c27aaca81112af1e59c8c0979.

With the patch applied I see that the cma area pool is misplaced which
cause my 4G device to fail to activate the cma pool. Below are some
logs:

*** Good case (6.12)

root@...t:~# dmesg|grep -i cma
[    0.000000] OF: reserved mem: initialized node linux,cma, compatible id shared-dma-pool
[    0.000000] OF: reserved mem: 0x0000000044200000..0x00000000541fffff (262144 KiB) map reusable linux,cma
[    0.056915] Memory: 3695024K/4194304K available (15552K kernel code, 2510K rwdata, 5992K rodata, 6016K init, 489K bss, 231772K reserved, 262144K cma-reserved)

*** Bad (6.12.16)

root@...t:~# dmesg|grep -i cma
[    0.000000] Reserved memory: created CMA memory pool at 0x00000000f2000000, size 256 MiB
[    0.000000] OF: reserved mem: initialized node linux,cma, compatible id shared-dma-pool
[    0.000000] OF: reserved mem: 0x00000000f2000000..0x0000000101ffffff (262144 KiB) map reusable linux,cma
[    0.056968] Memory: 3694896K/4194304K available (15616K kernel code, 2512K rwdata, 6012K rodata, 6080K init, 491K bss, 231900K reserved, 262144K cma-reserved)
[    0.116920] cma: CMA area linux,cma could not be activated

*** Good (6.12.16, revert 9a0fe62f93ed)

root@...t:~# dmesg|grep -i cma
[    0.000000] OF: reserved mem: initialized node linux,cma, compatible id shared-dma-pool
[    0.000000] OF: reserved mem: 0x0000000044200000..0x00000000541fffff (262144 KiB) map reusable linux,cma
[    0.060976] Memory: 3694896K/4194304K available (15616K kernel code, 2512K rwdata, 6012K rodata, 6080K init, 491K bss, 231900K reserved, 262144K cma-reserved)

Below is our reserved-memory dts node:

reserved-memory {
	#address-cells = <2>; 
	#size-cells = <2>; 
	ranges;

	linux,cma {
		compatible = "shared-dma-pool";
		reusable;
		/*
		 * The CMA area must be in the lower 32-bit address range.
		 */
		alloc-ranges = <0x0 0x42000000 0 0xc0000000>;
		size = <0x0 0x10000000>;
		alignment = <0 0x2000>;
		linux,cma-default;
	};

	optee-core@...00000 {
		reg = <0 0x40000000 0 0x1e00000>;
		no-map;
	};

	optee-shm@...00000 {
		reg = <0 0x41e00000 0 0x200000>;
		no-map;
	};

	m7_reserved: m7@...00000 {
		reg = <0 0x80000000 0 0x1000000>;
		no-map;
	};

	vdev0vring0: vdev0vring0@...00000 {
		reg = <0 0x55000000 0 0x8000>;
		no-map;
	};

	vdev0vring1: vdev0vring1@...08000 {
		reg = <0 0x55008000 0 0x8000>;
		no-map;
	};

	rsc_table: rsc-table@...ff000 {
		reg = <0 0x550ff000 0 0x1000>;
		no-map;
	};

	ram_console_buffer: ram-console-buffer@...00000 {
		reg = <0 0x55100000 0 0x1000>;
		no-map;
	};

	vdev0buffer: vdev0buffer@...00000 {
		compatible = "shared-dma-pool";
		reg = <0 0x55400000 0 0x100000>;
		no-map;
	};
};

My current workaround is to revert commit 9a0fe62f93ed and the
dep-chain: 2d1d620ff27b444 8de4e5a92282. But I would like to get a
proper solution without having revert commits in my downstream
patchstack.

Regards,
  Marco

Powered by blists - more mailing lists