linux-kernel - Re: [PATCH v4] RISC-V: Remove any memblock representing unusable memory area

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Message-ID: <mhng-93876e12-52f0-414a-bdea-1a2c06392854@palmerdabbelt-glaptop1>
Date:   Thu, 05 Nov 2020 10:03:58 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Atish Patra <Atish.Patra@....com>
CC:     linux-kernel@...r.kernel.org, Atish Patra <Atish.Patra@....com>,
        rppt@...ux.ibm.com, aou@...s.berkeley.edu,
        akpm@...ux-foundation.org, Anup Patel <Anup.Patel@....com>,
        linux-riscv@...ts.infradead.org, rppt@...nel.org,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject:     Re: [PATCH v4] RISC-V: Remove any memblock representing unusable memory area

On Wed, 07 Oct 2020 14:51:59 PDT (-0700), Atish Patra wrote:
> RISC-V limits the physical memory size by -PAGE_OFFSET. Any memory beyond
> that size from DRAM start is unusable. Just remove any memblock pointing
> to those memory region without worrying about computing the maximum size.
>
> Signed-off-by: Atish Patra <atish.patra@....com>
> Reviewed-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---
> Changes from v3->v4:
> 1. Rebased on top of for-next.
> ---
>  arch/riscv/mm/init.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 4eda1a7e8521..da43c17544c5 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -156,9 +156,8 @@ static void __init setup_initrd(void)
>
>  void __init setup_bootmem(void)
>  {
> -	phys_addr_t mem_size = 0;
> -	phys_addr_t total_mem = 0;
> -	phys_addr_t mem_start, start, end = 0;
> +	phys_addr_t mem_start = 0;
> +	phys_addr_t start, end = 0;
>  	phys_addr_t vmlinux_end = __pa_symbol(&_end);
>  	phys_addr_t vmlinux_start = __pa_symbol(&_start);
>  	u64 i;
> @@ -166,21 +165,18 @@ void __init setup_bootmem(void)
>  	/* Find the memory region containing the kernel */
>  	for_each_mem_range(i, &start, &end) {
>  		phys_addr_t size = end - start;
> -		if (!total_mem)
> +		if (!mem_start)
>  			mem_start = start;
>  		if (start <= vmlinux_start && vmlinux_end <= end)
>  			BUG_ON(size == 0);
> -		total_mem = total_mem + size;
>  	}
>
>  	/*
> -	 * Remove memblock from the end of usable area to the
> -	 * end of region
> +	 * The maximal physical memory size is -PAGE_OFFSET.
> +	 * Make sure that any memory beyond mem_start + (-PAGE_OFFSET) is removed
> +	 * as it is unusable by kernel.
>  	 */
> -	mem_size = min(total_mem, (phys_addr_t)-PAGE_OFFSET);
> -	if (mem_start + mem_size < end)
> -		memblock_remove(mem_start + mem_size,
> -				end - mem_start - mem_size);
> +	memblock_enforce_memory_limit(mem_start - PAGE_OFFSET);
>
>  	/* Reserve from the start of the kernel to the end of the kernel */
>  	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);

This is on fixes.  Thanks!