linux-kernel - Re: [PATCH v3] RISC-V: Remove any memblock representing unusable memory area

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Date:   Fri, 2 Oct 2020 15:42:23 +0530
From:   Anup Patel <anup@...infault.org>
To:     Atish Patra <atish.patra@....com>
Cc:     "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Zong Li <zong.li@...ive.com>
Subject: Re: [PATCH v3] RISC-V: Remove any memblock representing unusable
 memory area

On Fri, Oct 2, 2020 at 12:36 AM Atish Patra <atish.patra@....com> 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 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);
> --
> 2.25.1
>

Looks good to me.

Reviewed-by: Anup Patel <anup@...infault.org>

Regards,
Anup