linux-kernel - Re: [PATCH] riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping

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Date:   Tue, 4 Jul 2023 13:26:12 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
CC:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Song Shuai <suagrfillet@...il.com>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: Start of DRAM should at least be aligned on PMD
 size for the direct mapping

Hey Alex,

On Tue, Jul 04, 2023 at 02:18:37PM +0200, Alexandre Ghiti wrote:
> So that we do not end up mapping the whole linear mapping using 4K
> pages, which is slow at boot time, and also very likely at runtime.
> 
> So make sure we align the start of DRAM on a PMD boundary.
> 
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>

Obviously correct me if I am wrong here, but was this not reported by
Song Shuai as a regression?
Accordingly, should this not have Reported-by, Closes/Link & Fixes tags?

Cheers,
Conor.

> ---
>  arch/riscv/mm/init.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 4fa420faa780..4a43ec275c6d 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -214,8 +214,13 @@ static void __init setup_bootmem(void)
>  	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
>  
>  	phys_ram_end = memblock_end_of_DRAM();
> +
> +	/*
> +	 * Make sure we align the start of the memory on a PMD boundary so that
> +	 * at worst, we map the linear mapping with PMD mappings.
> +	 */
>  	if (!IS_ENABLED(CONFIG_XIP_KERNEL))
> -		phys_ram_base = memblock_start_of_DRAM();
> +		phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
>  
>  	/*
>  	 * In 64-bit, any use of __va/__pa before this point is wrong as we
> -- 
> 2.39.2
> 

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