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    Subject[PATCH 5.17 020/140] RISC-V: relocate DTB if its outside memory region
    Date
    From: Nick Kossifidis <mick@ics.forth.gr>

    commit c6fe81191bd74f7e6ae9ce96a4837df9485f3ab8 upstream.

    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@ics.forth.gr>
    Link: https://lore.kernel.org/r/20220322132839.3653682-1-mick@ics.forth.gr
    Tested-by: Conor Dooley <conor.dooley@microchip.com>
    Fixes: f105aa940e78 ("riscv: add BUILTIN_DTB support for MMU-enabled targets")
    Cc: stable@vger.kernel.org
    Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/riscv/mm/init.c | 21 +++++++++++++++++++--
    1 file changed, 19 insertions(+), 2 deletions(-)

    --- 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);

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