Re: [PATCH] x86/e820: apply 'mem=' boot command while reserving memory using boot_params

[Byungchul Park]

On Tue, Apr 23, 2024 at 07:13:23PM +0900, Byungchul Park wrote:
> I might miss something.  Please lemme know if I go wrong.  Thanks.
> 
> 	Byungchul
> 
> --->8---
> >From 51f3b5b9bf9685aa431c00908771151edd702483 Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul@xxxxxx>
> Date: Tue, 23 Apr 2024 18:54:48 +0900
> Subject: [PATCH] x86/e820: apply 'mem=' boot command while reserving memory
>  using boot_params
> 
> When a user specifies 'mem=' boot command, it's expected to limit the
> maximum address of usable memory for the kernel no matter what the
> memory map source is.  However, 'mem=' boot command doesn't work since
> it doesn't respect it when reserving memory using boot_params.
> 
> Applied the restriction when reserving memory using boot_params.  While
> at it, renamed mem_size to a more specific name, boot_mem_limit.
> 
> Signed-off-by: Byungchul Park <byungchul@xxxxxx>
> ---
>  arch/x86/kernel/e820.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index 6f1b379e3b38..af9d1d95ef5a 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -880,11 +880,11 @@ static void __init early_panic(char *msg)
>  
>  static int userdef __initdata;
>  
> +static u64 boot_mem_limit = U64_MAX;
> +
>  /* The "mem=nopentium" boot option disables 4MB page tables on 32-bit kernels: */
>  static int __init parse_memopt(char *p)
>  {
> -	u64 mem_size;
> -
>  	if (!p)
>  		return -EINVAL;
>  
> @@ -899,16 +899,16 @@ static int __init parse_memopt(char *p)
>  	}
>  
>  	userdef = 1;
> -	mem_size = memparse(p, &p);
> +	boot_mem_limit = memparse(p, &p);
>  
>  	/* Don't remove all memory when getting "mem={invalid}" parameter: */
> -	if (mem_size == 0)
> +	if (boot_mem_limit == 0)

I should've handled the case that the return value is 0.  I will fix it.
Before going ahead, it'd be appreciated to tell if this approach is
correct. Thank you.

	Byungchul

>  		return -EINVAL;
>  
> -	e820__range_remove(mem_size, ULLONG_MAX - mem_size, E820_TYPE_RAM, 1);
> +	e820__range_remove(boot_mem_limit, ULLONG_MAX - boot_mem_limit, E820_TYPE_RAM, 1);
>  
>  #ifdef CONFIG_MEMORY_HOTPLUG
> -	max_mem_size = mem_size;
> +	max_mem_size = boot_mem_limit;
>  #endif
>  
>  	return 0;
> @@ -1036,6 +1036,8 @@ void __init e820__reserve_setup_data(void)
>  		early_memunmap(data, len);
>  	}
>  
> +	e820__range_remove(boot_mem_limit, ULLONG_MAX - boot_mem_limit,
> +			E820_TYPE_RESERVED_KERN, 1);
>  	e820__update_table(e820_table);
>  
>  	pr_info("extended physical RAM map:\n");
> -- 
> 2.17.1