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Date:   Sun, 04 Oct 2020 16:22:00 -0700 (PDT)
Subject:     Re: [PATCH v3] RISC-V: Remove any memblock representing unusable memory area
In-Reply-To: <20201001190557.2860741-1-atish.patra@wdc.com>
CC:     linux-kernel@vger.kernel.org, Atish Patra <Atish.Patra@wdc.com>,
        rppt@linux.ibm.com, aou@eecs.berkeley.edu,
        Anup Patel <Anup.Patel@wdc.com>,
        linux-riscv@lists.infradead.org,
        Paul Walmsley <paul.walmsley@sifive.com>, zong.li@sifive.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     Atish Patra <Atish.Patra@wdc.com>
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On Thu, 01 Oct 2020 12:05:57 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@wdc.com>
> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
>
> ---
> Changes from v2->v3
> Updated comment as per Mike's suggestion.
> ---
>  arch/riscv/mm/init.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index ca03762a3733..564e0be677b7 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -146,8 +146,6 @@ static phys_addr_t dtb_early_pa __initdata;
>  void __init setup_bootmem(void)
>  {
>  	struct memblock_region *reg;
> -	phys_addr_t mem_size = 0;
> -	phys_addr_t total_mem = 0;
>  	phys_addr_t mem_start, end = 0;
>  	phys_addr_t vmlinux_end = __pa_symbol(&_end);
>  	phys_addr_t vmlinux_start = __pa_symbol(&_start);
> @@ -155,21 +153,18 @@ void __init setup_bootmem(void)
>  	/* Find the memory region containing the kernel */
>  	for_each_memblock(memory, reg) {
>  		end = reg->base + reg->size;
> -		if (!total_mem)
> +		if (!mem_start)
>  			mem_start = reg->base;
>  		if (reg->base <= vmlinux_start && vmlinux_end <= end)
>  			BUG_ON(reg->size == 0);
> -		total_mem = total_mem + reg->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);

Thanks, this is on for-next.