linux-kernel - Re: [PATCH] riscv: Allow to downgrade paging mode from the command line

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Message-ID: <87cz8m3sha.fsf@all.your.base.are.belong.to.us>
Date:   Wed, 14 Dec 2022 16:38:57 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Alexandre Ghiti <alexghiti@...osinc.com>,
        Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: Re: [PATCH] riscv: Allow to downgrade paging mode from the command
 line

Alexandre Ghiti <alexghiti@...osinc.com> writes:

> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index b56a0a75533f..8140fefe0e57 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -752,12 +752,35 @@ static void __init disable_pgtable_l4(void)
>   * then read SATP to see if the configuration was taken into account
>   * meaning sv48 is supported.
>   */
> -static __init void set_satp_mode(void)
> +static __init void set_satp_mode(uintptr_t dtb_pa)
>  {
>  	u64 identity_satp, hw_satp;
>  	uintptr_t set_satp_mode_pmd = ((unsigned long)set_satp_mode) & PMD_MASK;
>  	bool check_l4 = false;
>  
> +#ifndef CONFIG_KASAN
> +	/*
> +	 * The below fdt functions are kasan instrumented, since at this point
> +	 * there is no mapping for the kasan shadow memory, this can't be used
> +	 * when kasan is enabled.
> +	 */
> +	int chosen_node;
> +
> +	chosen_node = fdt_path_offset((void *)dtb_pa, "/chosen");
> +	if (chosen_node >= 0) {
> +		const char *cmdline = fdt_getprop((void *)dtb_pa, chosen_node,
> +						  "bootargs", NULL);

The command line handling needs to honor CONFIG_CMDLINE_FORCE and
CONFIG_CMDLINE_EXTEND (which makes it possible to use no{4,5}lvl *and*
KASAN ;-)).


Björn