Re: [PATCH RFC] arm64/mm: handle memmap kernel option

[Ard Biesheuvel]

On 25 February 2017 at 06:47, Yisheng Xie <xieyisheng1@xxxxxxxxxx> wrote:
> When use device tree mode, user can reserve memory by changes the dts,
> however, when boot with ACPI, user cannot reserve memory except by
> changing the ACPI table in BIOS, which is not so convenient.
>
> To make user reserve memory for some specific use more convenient,
> this patch implement the following memmap variants:
>  - memmap=nn[KMG]$ss[KMG]: mark specified memory as reserved;
>  - memmap=nn[KMG]@ss[KMG]: force usage of a specific region of memory;
>
> Reported-by: Bob Dong <dongbo4@xxxxxxxxxx>
> Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>

Could you explain which problem you are solving here? ACPI implies
UEFI on arm64, and so these reservations could be made by a boot
component instead, if it requires a fixed memory reservation. If this
is a reservation for, e.g., OP-TEE, we should not rely on the command
line to communicate this information.

> ---
>  arch/arm64/mm/init.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index e19e065..cf90c1d 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -188,6 +188,52 @@ static int __init early_mem(char *p)
>  }
>  early_param("mem", early_mem);
>
> +static void __init parse_memmap_one(char *p)
> +{
> +       char *oldp;
> +       unsigned long start_at, mem_size;
> +
> +       if (!p)
> +               return;
> +
> +       oldp = p;
> +       mem_size = memparse(p, &p);
> +       if (p == oldp)
> +               return;
> +
> +       switch (*p) {
> +       case '@':
> +               start_at = memparse(p + 1, &p);
> +               memblock_add(start_at, mem_size);
> +               break;
> +
> +       case '$':
> +               start_at = memparse(p + 1, &p);
> +               memblock_reserve(start_at, mem_size);
> +               break;
> +
> +       default:
> +               pr_warn("Unrecognized memmap syntax: %s\n", p);
> +               break;
> +       }
> +}
> +
> +static int __init parse_memmap_opt(char *str)
> +{
> +       while (str) {
> +               char *k = strchr(str, ',');
> +
> +               if (k)
> +                       *k++ = 0;
> +
> +               parse_memmap_one(str);
> +               str = k;
> +       }
> +
> +       return 0;
> +}
> +early_param("memmap", parse_memmap_opt);
> +
>  void __init arm64_memblock_init(void)
>  {
>         const s64 linear_region_size = -(s64)PAGE_OFFSET;
> --
> 1.7.12.4
>