linux-kernel - Re: [PATCH] RISC-V-fixes: relocate DTB if it's outside memory region

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Message-ID: <ebaa9b4e-9e37-e2f4-2bee-37d324e7302b@microchip.com>
Date:   Thu, 24 Mar 2022 09:37:29 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <mick@....forth.gr>, <palmer@...belt.com>
CC:     <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <paul.walmsley@...ive.com>, <aou@...s.berkeley.edu>
Subject: Re: [PATCH] RISC-V-fixes: relocate DTB if it's outside memory region


On 22/03/2022 13:28, Nick Kossifidis wrote:
> In case the DTB provided by the bootloader/BootROM is before the kernel
> image or outside /memory, we won't be able to access it through the
> linear mapping, and get a segfault on setup_arch(). Currently OpenSBI
> relocates DTB but that's not always the case (e.g. if FW_JUMP_FDT_ADDR
> is not specified), and it's also not the most portable approach since
> the default FW_JUMP_FDT_ADDR of the generic platform relocates the DTB
> at a specific offset that may not be available. To avoid this situation
> copy DTB so that it's visible through the linear mapping.
> 
> Signed-off-by: Nick Kossifidis <mick@....forth.gr>

Albeit in a backport, I tested this on a PolarFire SoC based board.
So I guess, Tested-by: Conor Dooley <conor.dooley@...rochip.com>

And a lot cleaner than using create_pgd_mapping in setup_vm_final to do it :)

Thanks,
Conor.

> ---
>   arch/riscv/mm/init.c | 21 +++++++++++++++++++--
>   1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 0d588032d..697a9aed4 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -206,8 +206,25 @@ 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))
> -		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> +	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));
> +	}
>   
>   	early_init_fdt_scan_reserved_mem();
>   	dma_contiguous_reserve(dma32_phys_limit);