[PATCH 2/2] riscv: Add mem kernel parameter support

[Palmer Dabbelt]

On Wed, 02 Jun 2021 01:55:17 PDT (-0700), wangkefeng.wang at huawei.com wrote:
> The memblock_enforce_memory_limit() could change the memblock
> range, so move the dram_end assignment after it in bootmem_init(),
> then support mem= cmdline.
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang at huawei.com>
> ---
>  arch/riscv/mm/init.c | 29 +++++++++++++++++++++++++----
>  1 file changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 17f2e1da2b3d..ce61510a08c0 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -127,19 +127,39 @@ void __init mem_init(void)
>  	print_vm_layout();
>  }
>
> +/*
> + * The default maximal physical memory size is -PAGE_OFFSET,
> + * limit the memory size via mem.
> + */
> +static phys_addr_t memory_limit = -PAGE_OFFSET;
> +
> +static int __init early_mem(char *p)
> +{
> +	u64 size;
> +
> +	if (!p)
> +		return 1;
> +
> +	size = memparse(p, &p) & PAGE_MASK;
> +	memory_limit = min_t(u64, size, memory_limit);
> +
> +	pr_notice("Memory limited to %lldMB\n", (u64)memory_limit >> 20);
> +
> +	return 0;
> +}
> +early_param("mem", early_mem);
> +
>  void __init setup_bootmem(void)
>  {
>  	phys_addr_t vmlinux_end = __pa_symbol(&_end);
>  	phys_addr_t vmlinux_start = __pa_symbol(&_start);
> -	phys_addr_t dram_end = memblock_end_of_DRAM();
>  	phys_addr_t max_mapped_addr = __pa(~(ulong)0);
> +	phys_addr_t dram_end;
>
>  #ifdef CONFIG_XIP_KERNEL
>  	vmlinux_start = __pa_symbol(&_sdata);
>  #endif
> -
> -	/* The maximal physical memory size is -PAGE_OFFSET. */
> -	memblock_enforce_memory_limit(-PAGE_OFFSET);
> +	memblock_enforce_memory_limit(memory_limit);
>
>  	/*
>  	 * Reserve from the start of the kernel to the end of the kernel
> @@ -154,6 +174,7 @@ void __init setup_bootmem(void)
>  #endif
>  	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
>
> +	dram_end = memblock_end_of_DRAM();
>  	/*
>  	 * memblock allocator is not aware of the fact that last 4K bytes of
>  	 * the addressable memory can not be mapped because of IS_ERR_VALUE

I'm not sure why, but this patch won't apply.  I've applied it manually, 
it's on for-next (along with the #1).

Thanks!