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

From: Palmer Dabbelt
Date: Fri Apr 29 2022 - 11:29:07 EST


On Thu, 28 Apr 2022 14:48:14 PDT (-0700), Palmer Dabbelt wrote:
On Mon, 25 Apr 2022 23:11:23 PDT (-0700), mick@xxxxxxxxxxxx wrote:
Hello Palmer,

Any updates on this ?

Sorry about that, it's on fixes.

Not sure if I just wasn't paying attention yesterday or if I'm grumpier this morning, but that "RISC-V-fixes: " prefix is just a bit too odd -- I know we've got a split between "RISC-V" and "riscv" so maybe it doesn't matter, but even that is kind of ugly.

I re-wrote it, but I'm going to let it round trip through linux-next so I'll send it up next time.

Sorry, I know this happened twice recently but I'll try not to make a habit of it.



Regards,
Nick

On 3/22/22 15:28, 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@xxxxxxxxxxxx>
---
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);