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

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Date:   Tue, 22 Mar 2022 15:28:39 +0200
From:   Nick Kossifidis <mick@....forth.gr>
To:     palmer@...belt.com, paul.walmsley@...ive.com, aou@...s.berkeley.edu
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Nick Kossifidis <mick@....forth.gr>
Subject: [PATCH] RISC-V-fixes: relocate DTB if it's outside memory region

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>
---
 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);
-- 
2.34.1