linux-kernel - Re: [PATCH 02/12] RISC-V: MAXPHYSMEM_2GB doesn't depend on CMODEL

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Date:   Sat, 20 Nov 2021 09:27:09 +0530
From:   Anup Patel <anup@...infault.org>
To:     Palmer Dabbelt <palmer@...osinc.com>
Cc:     linux-riscv <linux-riscv@...ts.infradead.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Atish Patra <atish.patra@....com>,
        Bin Meng <bin.meng@...driver.com>,
        Sagar Shrikant Kadam <sagar.kadam@...ive.com>,
        Damien Le Moal <damien.lemoal@....com>, axboe@...nel.dk,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 02/12] RISC-V: MAXPHYSMEM_2GB doesn't depend on CMODEL_MEDLOW

On Fri, Nov 19, 2021 at 10:14 PM Palmer Dabbelt <palmer@...osinc.com> wrote:
>
> From: Palmer Dabbelt <palmer@...osinc.com>
>
> For non-relocatable kernels we need to be able to link the kernel at
> approximately PAGE_OFFSET, thus requiring medany (as medlow requires the
> code to be linked within 2GiB of 0).  The inverse doesn't apply, though:
> since medany code can be linked anywhere it's fine to link it close to
> 0, so we can support the smaller memory config.
>
> Fixes: de5f4b8f634b ("RISC-V: Define MAXPHYSMEM_1GB only for RV32")
> Cc: stable@...r.kernel.org
> Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>

Looks good to me.

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

Regards,
Anup

>
> ---
>
> I found this when going through the savedefconfig diffs for the K210
> defconfigs.  I'm not entirely sure they're doing the right thing here
> (they should probably be setting CMODEL_LOW to take advantage of the
> better code generation), but I don't have any way to test those
> platforms so I don't want to change too much.
> ---
>  arch/riscv/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 821252b65f89..61f64512dcde 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -280,7 +280,7 @@ choice
>                 depends on 32BIT
>                 bool "1GiB"
>         config MAXPHYSMEM_2GB
> -               depends on 64BIT && CMODEL_MEDLOW
> +               depends on 64BIT
>                 bool "2GiB"
>         config MAXPHYSMEM_128GB
>                 depends on 64BIT && CMODEL_MEDANY
> --
> 2.32.0
>