linux-kernel - Re: [PATCH -fixes v2 3/3] riscv: No need to relocate the dtb as it lies in the fixmap region

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Date:   Wed, 29 Mar 2023 14:56:45 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Conor Dooley <conor.dooley@...rochip.com>,
        linux-doc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -fixes v2 3/3] riscv: No need to relocate the dtb as it
 lies in the fixmap region

On Wed, Mar 29, 2023 at 10:19:32AM +0200, Alexandre Ghiti wrote:
> We used to access the dtb via its linear mapping address but now that the
> dtb early mapping was moved in the fixmap region, we can keep using this
> address since it is present in swapper_pg_dir, and remove the dtb
> relocation.
> 
> Note that the relocation was wrong anyway since early_memremap() is
> restricted to 256K whereas the maximum fdt size is 2MB.

So, should this be marked as a fix, and backported along with 1/3?
Either way,
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

And from v1 (although I didn't actually send it for idk what reason):
Tested-by: Conor Dooley <conor.dooley@...rochip.com>

Thanks,
Conor.

> 
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
>  arch/riscv/mm/init.c | 21 ++-------------------
>  1 file changed, 2 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index fb78d6bbabae..0f14f4a8d179 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -249,25 +249,8 @@ static void __init setup_bootmem(void)
>  	 * early_init_fdt_reserve_self() since __pa() does
>  	 * not work for DTB pointers that are fixmap addresses
>  	 */
> -	if (!IS_ENABLED(CONFIG_BUILTIN_DTB)) {
> -		/*
> -		 * In case the DTB is not located in a memory region we won't
> -		 * be able to locate it later on via the linear mapping and
> -		 * get a segfault when accessing it via __va(dtb_early_pa).
> -		 * To avoid this situation copy DTB to a memory region.
> -		 * Note that memblock_phys_alloc will also reserve DTB region.
> -		 */
> -		if (!memblock_is_memory(dtb_early_pa)) {
> -			size_t fdt_size = fdt_totalsize(dtb_early_va);
> -			phys_addr_t new_dtb_early_pa = memblock_phys_alloc(fdt_size, PAGE_SIZE);
> -			void *new_dtb_early_va = early_memremap(new_dtb_early_pa, fdt_size);
> -
> -			memcpy(new_dtb_early_va, dtb_early_va, fdt_size);
> -			early_memunmap(new_dtb_early_va, fdt_size);
> -			_dtb_early_pa = new_dtb_early_pa;
> -		} else
> -			memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> -	}
> +	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))
> -- 
> 2.37.2
> 

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