linux-kernel - Re: [PATCH] arm64: mm: add support for memmap kernel parameters

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Message-ID: <20201118173854.GA8537@kernel.org>
Date:   Wed, 18 Nov 2020 19:38:54 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Barry Song <song.bao.hua@...ilicon.com>
Cc:     catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, anshuman.khandual@....com,
        linuxarm@...wei.com
Subject: Re: [PATCH] arm64: mm: add support for memmap kernel parameters

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]$ss[KMG]
> Region of memory to be reserved is from ss to ss+nn
> 
> If users set memmap=exactmap before memmap=nn[KMG]@ss[KMG], they will
> get the exact memory specified by memmap=nn[KMG]@ss[KMG]. For example,
> on one machine with 4GB memory, "memmap=exactmap memmap=1G@1G" will
> make kernel use the memory from 1GB to 2GB only.
> 
> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> ---
>  arch/arm64/mm/init.c | 59 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 59 insertions(+)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 095540667f0f..f1c6bfdbc953 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -235,6 +235,65 @@ static int __init early_mem(char *p)
>  }
>  early_param("mem", early_mem);
>  
> +static int need_remove_real_memblock __initdata;
> +
> +static void __init parse_memmap_one(char *p)
> +{
> +	char *oldp;
> +	unsigned long start_at, mem_size;
> +
> +	if (!p)
> +		return;
> +
> +	if (!strncmp(p, "exactmap", 8)) {
> +		need_remove_real_memblock = 1;
> +		return;
> +	}
> +
> +	oldp = p;
> +	mem_size = memparse(p, &p);
> +	if (p == oldp)
> +		return;
> +
> +	switch (*p) {
> +	case '@':
> +		start_at = memparse(p + 1, &p);
> +		/*
> +		 * use the exactmap defined by nn[KMG]@ss[KMG], remove
> +		 * memblock populated by DT etc.
> +		 */
> +		if (need_remove_real_memblock) {
> +			need_remove_real_memblock = 0;
> +			memblock_remove(0, ULLONG_MAX);
> +		}
> +		memblock_add(start_at, mem_size);
> +		break;
> +	case '$':
> +		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.