Re: [PATCH v2 3/4] MIPS: Refactor early_parse_memmap() to fix memmap= parameter

[Mike Rapoport <rppt@kernel.org>]

On Mon, Feb 28, 2022 at 02:31:05PM +0800, Tiezhu Yang wrote:
> According to Documentation/admin-guide/kernel-parameters.txt,
> the kernel command-line parameter memmap= means "Force usage
> of a specific region of memory", but when add "memmap=3G@64M"
> to the command-line, kernel boot hangs in sparse_init().
> 
> In order to support memmap=limit@base, refactor the function
> early_parse_memmap() and then use memblock_mem_range_remove_map()
> to limit the memory region.
> 
> With this patch, when add "memmap=3G@64M" to the command-line,
> the kernel boots successfully, we can see the following messages:
> 
>   [    0.000000] Memory limited to 64MB-3136MB
>   ...
>   [    0.000000] Early memory node ranges
>   [    0.000000]   node   0: [mem 0x0000000004000000-0x000000000effffff]
>   [    0.000000]   node   0: [mem 0x0000000090200000-0x00000000ffffffff]
>   [    0.000000]   node   0: [mem 0x0000000120000000-0x00000001653fffff]
>   ...
>   [    0.000000] Memory: 3070816K/3147776K available (...)
> 
> When add "memmap=128M@64M nr_cpus=1 init 3" to the command-line,
> the kernel also boots successfully, we can see the following messages:
> 
>   [    0.000000] Memory limited to 64MB-192MB
>   ...
>   [    0.000000] Early memory node ranges
>   [    0.000000]   node   0: [mem 0x0000000004000000-0x000000000c1fffff]
>   ...
>   [    0.000000] Memory: 95312K/133120K available (...)
> 
> After login, the output of free command is consistent with the
> above log.
> 
> By the way, this commit only supports memmap=limit@base format,
> the other formats such as memmap=limit#base, memmap=limit$base
> and memmap=limit!base can be added if they are necessary in the
> future.
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  arch/mips/kernel/setup.c | 42 +++++++++---------------------------------
>  1 file changed, 9 insertions(+), 33 deletions(-)
> 
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 6b6d718..e3b1f2e 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -340,6 +340,7 @@ static void __init bootmem_init(void)
>  
>  static int usermem __initdata;
>  static phys_addr_t memory_limit;
> +static phys_addr_t memory_base;
>  
>  static int __init early_parse_mem(char *p)
>  {
> @@ -355,42 +356,17 @@ early_param("mem", early_parse_mem);
>  
>  static int __init early_parse_memmap(char *p)
>  {
> -	char *oldp;
> -	u64 start_at, mem_size;
> -
>  	if (!p)
> -		return -EINVAL;
> +		return 1;
>  
> -	if (!strncmp(p, "exactmap", 8)) {
> -		pr_err("\"memmap=exactmap\" invalid on MIPS\n");
> -		return 0;
> -	}
> +	memory_limit = memparse(p, &p) & PAGE_MASK;
> +	if (*p == '@')
> +		memory_base = memparse(p + 1, &p) & PAGE_MASK;
>  
> -	oldp = p;
> -	mem_size = memparse(p, &p);
> -	if (p == oldp)
> -		return -EINVAL;
> -
> -	if (*p == '@') {
> -		start_at = memparse(p+1, &p);
> -		memblock_add(start_at, mem_size);
> -	} else if (*p == '#') {
> -		pr_err("\"memmap=nn#ss\" (force ACPI data) invalid on MIPS\n");
> -		return -EINVAL;
> -	} else if (*p == '$') {
> -		start_at = memparse(p+1, &p);
> -		memblock_add(start_at, mem_size);
> -		memblock_reserve(start_at, mem_size);
> -	} else {
> -		pr_err("\"memmap\" invalid format!\n");
> -		return -EINVAL;

This breaks backward compatibility for systems that use memmap=X#Y and
memmap=X$Y.

For your use case it is enough to implement "memmap=exactmap" that will
drop memory provided by the firmware and only use ranges supplied in
memmap=

> -	}
> +	pr_notice("Memory limited to %lldMB-%lldMB\n",
> +		  memory_base >> 20, (memory_base + memory_limit) >> 20);
>  
> -	if (*p == '\0') {
> -		usermem = 1;
> -		return 0;
> -	} else
> -		return -EINVAL;
> +	return 0;
>  }
>  early_param("memmap", early_parse_memmap);
>  
> @@ -667,7 +643,7 @@ static void __init arch_mem_init(char **cmdline_p)
>  		__pa_symbol(&__nosave_end) - __pa_symbol(&__nosave_begin));
>  
>  	/* Limit the memory. */
> -	memblock_enforce_memory_limit(memory_limit);
> +	memblock_mem_range_remove_map(memory_base, memory_limit);
>  	memblock_allow_resize();
>  
>  	early_memtest(PFN_PHYS(ARCH_PFN_OFFSET), PFN_PHYS(max_low_pfn));
> -- 
> 2.1.0
> 

-- 
Sincerely yours,
Mike.