Hi Barry,
On Wed, Nov 18, 2020 at 07:33:14PM +1300, Barry Song wrote:
> memmap should be an useful kernel parameter which has been supported by
> x86, mips and xtensa.
Why is this parameter should be useful for ARM64?
My understanding is that it is required only to work around really
broken bootloaders, isn't it?
> This patch adds support for ARM64. At this stage,
> the below two modes are supported only:
> memmap=nn[KMG]@ss[KMG]
> Force usage of a specific region of memory
>
> memmap=nn[KMG]$ss[KMG]
> Region of memory to be reserved is from ss to ss+nn
>
> If users set memmap=exactmap before memmap=nn[KMG]@ss[KMG], they will
> get the exact memory specified by memmap=nn[KMG]@ss[KMG]. For example,
> on one machine with 4GB memory, "memmap=exactmap memmap=1G@1G" will
> make kernel use the memory from 1GB to 2GB only.
>
> Signed-off-by: Barry Song <song.bao....@hisilicon.com>
> ---
> arch/arm64/mm/init.c | 59 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 59 insertions(+)
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 095540667f0f..f1c6bfdbc953 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -235,6 +235,65 @@ static int __init early_mem(char *p)
> }
> early_param("mem", early_mem);
>
> +static int need_remove_real_memblock __initdata;
> +
> +static void __init parse_memmap_one(char *p)
> +{
> + char *oldp;
> + unsigned long start_at, mem_size;
> +
> + if (!p)
> + return;
> +
> + if (!strncmp(p, "exactmap", 8)) {
> + need_remove_real_memblock = 1;
> + return;
> + }
> +
> + oldp = p;
> + mem_size = memparse(p, &p);
> + if (p == oldp)
> + return;
> +
> + switch (*p) {
> + case '@':
> + start_at = memparse(p + 1, &p);
> + /*
> + * use the exactmap defined by nn[KMG]@ss[KMG], remove
> + * memblock populated by DT etc.
> + */
> + if (need_remove_real_memblock) {
> + need_remove_real_memblock = 0;
> + memblock_remove(0, ULLONG_MAX);
> + }
> + memblock_add(start_at, mem_size);
> + break;
> + case '$':
> + 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);
> +
> static int __init early_init_dt_scan_usablemem(unsigned long node,
> const char *uname, int depth, void *data)
> {
> --
> 2.25.1
>
--
Sincerely yours,
Mike.
