linux-kernel - [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 10:19:32 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     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
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH -fixes v2 3/3] riscv: No need to relocate the dtb as it lies in the fixmap region

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.

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