linux-kernel - [PATCH 2/3] arm64: mm: Make map

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Message-ID: <20250822041538.467514-3-CFSworks@gmail.com>
Date: Thu, 21 Aug 2025 21:15:37 -0700
From: Sam Edwards <cfsworks@...il.com>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Marc Zyngier <maz@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Baruch Siach <baruch@...s.co.il>,
	Kevin Brodsky <kevin.brodsky@....com>,
	Joey Gouly <joey.gouly@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Sam Edwards <CFSworks@...il.com>
Subject: [PATCH 2/3] arm64: mm: Make map_fdt() return mapped pointer

Currently map_fdt() accepts a physical address and relies on the caller
to keep using the same value after mapping, since the implementation
happens to install an identity mapping. This obscures the fact that the
usable pointer is defined by the mapping, not by the input value. Since
the mapping determines pointer validity, it is more natural to produce
the pointer at mapping time.

Change map_fdt() to return a void * pointing to the mapped FDT. This
clarifies the data flow, removes the implicit identity assumption, and
prepares for making map_fdt() accept a phys_addr_t in a follow-up
change.

Signed-off-by: Sam Edwards <CFSworks@...il.com>
---
 arch/arm64/kernel/pi/map_kernel.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/pi/map_kernel.c b/arch/arm64/kernel/pi/map_kernel.c
index 2b3047860230..5dc4107b5a7f 100644
--- a/arch/arm64/kernel/pi/map_kernel.c
+++ b/arch/arm64/kernel/pi/map_kernel.c
@@ -191,7 +191,7 @@ static void __init remap_idmap_for_lpa2(void)
 	memset(init_pg_dir, 0, (char *)init_pg_end - (char *)init_pg_dir);
 }
 
-static void __init map_fdt(u64 fdt)
+static void *__init map_fdt(u64 fdt)
 {
 	static u8 ptes[INIT_IDMAP_FDT_SIZE] __initdata __aligned(PAGE_SIZE);
 	u64 efdt = fdt + MAX_FDT_SIZE;
@@ -205,6 +205,8 @@ static void __init map_fdt(u64 fdt)
 		  fdt, PAGE_KERNEL, IDMAP_ROOT_LEVEL,
 		  (pte_t *)init_idmap_pg_dir, false, 0);
 	dsb(ishst);
+
+	return (void *)fdt;
 }
 
 /*
@@ -238,15 +240,14 @@ asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
 	int root_level = 4 - CONFIG_PGTABLE_LEVELS;
 	int va_bits = VA_BITS;
 	int chosen;
-
-	map_fdt((u64)fdt);
+	void *fdt_mapped = map_fdt((u64)fdt);
 
 	/* Clear BSS and the initial page tables */
 	memset(__bss_start, 0, (char *)init_pg_end - (char *)__bss_start);
 
 	/* Parse the command line for CPU feature overrides */
-	chosen = fdt_path_offset(fdt, chosen_str);
-	init_feature_override(boot_status, fdt, chosen);
+	chosen = fdt_path_offset(fdt_mapped, chosen_str);
+	init_feature_override(boot_status, fdt_mapped, chosen);
 
 	if (IS_ENABLED(CONFIG_ARM64_64K_PAGES) && !cpu_has_lva()) {
 		va_bits = VA_BITS_MIN;
@@ -266,7 +267,7 @@ asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
 	 * fill in the high bits from the seed.
 	 */
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
-		u64 kaslr_seed = kaslr_early_init(fdt, chosen);
+		u64 kaslr_seed = kaslr_early_init(fdt_mapped, chosen);
 
 		if (kaslr_seed && kaslr_requires_kpti())
 			arm64_use_ng_mappings = ng_mappings_allowed();
-- 
2.49.1