linux-kernel - Re: [PATCH] riscv: reserve DTB before possible memblock allocation

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Message-ID: <20230607-jogging-grudging-70dede86bc53@spud>
Date:   Wed, 7 Jun 2023 19:17:28 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Woody Zhang <woodylab@...mail.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        alexghiti@...osinc.com
Subject: Re: [PATCH] riscv: reserve DTB before possible memblock allocation

+CC Alex, you should take a look at this patch.

On Wed, Jun 07, 2023 at 09:35:19PM +0800, Woody Zhang wrote:
> It's possible that early_init_fdt_scan_reserved_mem() allocates memory
> from memblock for dynamic reserved memory in `/reserved-memory` node.
> Any fixed reservation must be done before that to avoid potential
> conflicts.
> 
> Reserve the DTB in memblock just after early scanning it.

The rationale makes sense to me, I am just wondering what compelling
reason there is to move it away from the memblock_reserve()s for the
initd and vmlinux? Moving it above early_init_fdt_scan_reserved_mem()
should be the sufficient minimum & would keep things together.

Cheers,
Conor.

> 
> Signed-off-by: Woody Zhang <woodylab@...mail.com>
> ---
>  arch/riscv/kernel/setup.c | 10 ++++++++++
>  arch/riscv/mm/init.c      |  9 ---------
>  2 files changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 36b026057503..c147fa8da929 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -16,6 +16,7 @@
>  #include <linux/console.h>
>  #include <linux/screen_info.h>
>  #include <linux/of_fdt.h>
> +#include <linux/libfdt.h>
>  #include <linux/sched/task.h>
>  #include <linux/smp.h>
>  #include <linux/efi.h>
> @@ -256,6 +257,15 @@ static void __init parse_dtb(void)
>  		pr_err("No DTB passed to the kernel\n");
>  	}
>  
> +	/*
> +	 * If DTB is built in, no need to reserve its memblock.
> +	 * Otherwise, do reserve it but avoid using
> +	 * early_init_fdt_reserve_self() since __pa() does
> +	 * not work for DTB pointers that are fixmap addresses
> +	 */
> +	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
> +		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> +
>  #ifdef CONFIG_CMDLINE_FORCE
>  	strscpy(boot_command_line, CONFIG_CMDLINE, COMMAND_LINE_SIZE);
>  	pr_info("Forcing kernel command line to: %s\n", boot_command_line);
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index c6bb966e4123..f8c9a79acd94 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -254,15 +254,6 @@ static void __init setup_bootmem(void)
>  	 */
>  	early_init_fdt_scan_reserved_mem();
>  
> -	/*
> -	 * If DTB is built in, no need to reserve its memblock.
> -	 * Otherwise, do reserve it but avoid using
> -	 * early_init_fdt_reserve_self() since __pa() does
> -	 * not work for DTB pointers that are fixmap addresses
> -	 */
> -	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
> -		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> -
>  	dma_contiguous_reserve(dma32_phys_limit);
>  	if (IS_ENABLED(CONFIG_64BIT))
>  		hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT);
> -- 
> 2.39.2
> 

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