Re: [PATCH v7 1/2] of: reserved_mem: Restruture how the reserved memory regions are processed

[Rob Herring <robh@kernel.org>]

On Fri, Aug 9, 2024 at 1:48 PM Oreoluwa Babatunde
<quic_obabatun@quicinc.com> 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.
>    - Call the region specific initialization function for the region
>      using fdt_init_reserved_mem_node().
>
> 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().
>
> 2) This step is also moved to be after the page tables have been
>    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@quicinc.com>
> ---
>  drivers/of/fdt.c             |   5 +-
>  drivers/of/of_private.h      |   3 +-
>  drivers/of/of_reserved_mem.c | 172 +++++++++++++++++++++++++----------
>  3 files changed, 131 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 68103ad230ee..d4b7aaa70e31 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -511,8 +511,6 @@ void __init early_init_fdt_scan_reserved_mem(void)
>                         break;
>                 memblock_reserve(base, size);
>         }
> -
> -       fdt_init_reserved_mem();
>  }
>
>  /**
> @@ -1239,6 +1237,9 @@ void __init unflatten_device_tree(void)
>         of_alias_scan(early_init_dt_alloc_memory_arch);
>
>         unittest_unflatten_overlay_base();
> +
> +       /* Save the statically-placed regions in the reserved_mem array */
> +       fdt_scan_reserved_mem_reg_nodes();

I'm still not understanding why the unflatttened API doesn't work
here? It was just used in of_alias_scan() above here.

The problem reported is this function uses initial_boot_params, but
that's NULL for x86.

Rob