[PATCH v9 07/11] arm: armv8: mmu: add mmu_unmap_reserved_mem

[Ilias Apalodimas]

Hi Anshul,

On Fri, 10 Oct 2025 at 08:54, Anshul Dalal <anshuld at ti.com> wrote:
>
> For armv8, U-Boot uses a static map defined as 'mem_map' for configuring
> the MMU's page tables, done by mmu_setup.
>
> Though this works well for simpler platforms, it makes creating runtime
> carveouts by modifying the static array at runtime exceedingly complex
> like in mach-snapdragon/board.c.
>
> Creation of such carveouts is much better handled by APIs such as
> mmu_change_region_attr once the page tables are configured. Usually such
> carveouts are configured via the device-tree's reserved-memory node
> which provides the address and size for the carveout.
>
> Therefore this patch adds mmu_unmap_reserved_mem which acts as a wrapper
> over mmu_change_region_attr, helping unmap a reserved-memory region.
>
> Signed-off-by: Anshul Dalal <anshuld at ti.com>
> Tested-by: Wadim Egorov <w.egorov at phytec.de>
> ---
>  arch/arm/cpu/armv8/cache_v8.c    | 23 +++++++++++++++++++++++
>  arch/arm/include/asm/armv8/mmu.h |  9 +++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
> index cdf17d5f396..74814601483 100644
> --- a/arch/arm/cpu/armv8/cache_v8.c
> +++ b/arch/arm/cpu/armv8/cache_v8.c
> @@ -86,6 +86,29 @@ int mem_map_fix_dram_banks(unsigned int index, unsigned int len, u64 attrs)
>
>         return 0;
>  }
> +
> +int mmu_unmap_reserved_mem(const char *name)
> +{
> +       void *fdt = (void *)gd->fdt_blob;
> +       char node_path[128];
> +       fdt_addr_t addr;
> +       fdt_size_t size;
> +       int ret;
> +
> +       snprintf(node_path, sizeof(node_path), "/reserved-memory/%s", name);
> +       ret = fdt_path_offset(fdt, node_path);
> +       if (ret < 0)
> +               return ret;

The DT spec defines a /reserved/ no-map; option for reserved memory
that should not participate in the memory map.
Is there any reason why we unconditionally unmap reserved memory and
not the no-map one only?

Cheers
/Ilias
> +
> +       addr = fdtdec_get_addr_size(fdt, ret, "reg", &size);
> +       if (addr == FDT_ADDR_T_NONE)
> +               return -1;
> +
> +       mmu_change_region_attr_nobreak(addr, size, PTE_TYPE_FAULT);
> +
> +       return 0;
> +}
> +
>  u64 get_tcr(u64 *pips, u64 *pva_bits)
>  {
>         int el = get_effective_el();
> diff --git a/arch/arm/include/asm/armv8/mmu.h b/arch/arm/include/asm/armv8/mmu.h
> index 257352f216e..fbd64e649ff 100644
> --- a/arch/arm/include/asm/armv8/mmu.h
> +++ b/arch/arm/include/asm/armv8/mmu.h
> @@ -206,6 +206,15 @@ void setup_pgtables(void);
>   * @len: The size of mem_map
>   */
>  int mem_map_fix_dram_banks(unsigned int index, unsigned int len, u64 attrs);
> +
> +/**
> + * mmu_unmap_reserved_mem() - Unmaps a reserved-memory node as PTE_TYPE_FAULT
> + * once MMU is configured by mmu_setup.
> + *
> + * @name: The name of the node under "/reserved-memory/" path
> + */
> +int mmu_unmap_reserved_mem(const char *name);
> +
>  u64 get_tcr(u64 *pips, u64 *pva_bits);
>
>  /**
> --
> 2.51.0
>