[PATCH 2/2] arm64: mm: support bootparam max_addr

[Ard Biesheuvel]

On Wed, 15 Dec 2021 at 07:56, Peng Fan (OSS) <peng.fan at oss.nxp.com> wrote:
>
> From: Peng Fan <peng.fan at nxp.com>
>
> There is a "mem=[x]" boot parameter, but when there is a whole reserved
> by secure TEE, the continuous DRAM area is split with two memblocks.
>
> For example, DRAM area [0x40000000, 0xffffffff], when TEE uses
> [0x50000000, 0x51000000), the memblock will be split into
> [0x40000000, 0x50000000) and [0x51000000, 0xffffffff].
>
> If pass "mem=1024MB", the actually max addr will be 0x81000000.
> However if need the max addr be 0x80000000, mem=1008MB should be used.
>
> There also might be multiple other holes that no visible to Linux, when
> we wanna to limit the max addr usable by Linux, using "max_addr=[X]" is
> much easier than "mem=[X]"
>
> Signed-off-by: Peng Fan <peng.fan at nxp.com>

mem= is a hack already, please don't add another one. Limiting the
memory like this is far too tricky, given that the kernel itself and
the initrd could end up in memory that is excluded, and we have to go
and fix things up if that happens.


> ---
>  arch/arm64/mm/init.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index db63cc885771..3364b5e7a7fe 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -173,6 +173,7 @@ int pfn_is_map_memory(unsigned long pfn)
>  EXPORT_SYMBOL(pfn_is_map_memory);
>
>  static phys_addr_t memory_limit __ro_after_init = PHYS_ADDR_MAX;
> +static phys_addr_t max_addr __ro_after_init = PHYS_ADDR_MAX;
>
>  /*
>   * Limit the memory size that was specified via FDT.
> @@ -189,6 +190,18 @@ static int __init early_mem(char *p)
>  }
>  early_param("mem", early_mem);
>
> +static int __init set_max_addr(char *p)
> +{
> +       if (!p)
> +               return 1;
> +
> +       max_addr = memparse(p, &p) & PAGE_MASK;
> +       pr_notice("Memory max addr set to 0x%llx\n", max_addr);
> +
> +       return 0;
> +}
> +early_param("max_addr", set_max_addr);
> +
>  void __init arm64_memblock_init(void)
>  {
>         s64 linear_region_size = PAGE_END - _PAGE_OFFSET(vabits_actual);
> @@ -253,6 +266,9 @@ void __init arm64_memblock_init(void)
>                 memblock_add(__pa_symbol(_text), (u64)(_end - _text));
>         }
>
> +       if (max_addr != PHYS_ADDR_MAX)
> +               memblock_cap_memory_range(0, max_addr);
> +
>         if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size) {
>                 /*
>                  * Add back the memory we just removed if it results in the
> @@ -427,4 +443,9 @@ void dump_mem_limit(void)
>         } else {
>                 pr_emerg("Memory Limit: none\n");
>         }
> +
> +       if (max_addr != PHYS_ADDR_MAX)
> +               pr_emerg("Max addr: 0x%llx\n", max_addr);
> +       else
> +               pr_emerg("Max addr: none\n");
>  }
> --
> 2.25.1
>
>
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