linux-kernel - [PATCH 3/3] arm64/ptdump: Add 'early_ptdump' kernel command line option

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Message-Id: <20250910094623.2356282-4-anshuman.khandual@arm.com>
Date: Wed, 10 Sep 2025 15:16:23 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Anshuman Khandual <anshuman.khandual@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Ritesh Harjani <ritesh.list@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org
Subject: [PATCH 3/3] arm64/ptdump: Add 'early_ptdump' kernel command line option

Enable kernel pgtable dump during boot via a new kernel command line option
'early_ptdump'. This calls ptdump_walk() during boot right after ptdump has
been initialized with ptdump_init().

Cc: Jonathan Corbet <corbet@....net>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org
Suggested-by: Ryan Roberts <ryan.roberts@....com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 Documentation/admin-guide/kernel-parameters.txt |  4 ++++
 arch/arm64/include/asm/ptdump.h                 |  2 ++
 arch/arm64/kernel/setup.c                       |  1 +
 arch/arm64/mm/ptdump.c                          | 16 ++++++++++++++++
 4 files changed, 23 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 747a55abf494..f8e916750e2e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1295,6 +1295,10 @@
 			Enable debug messages in early_ioremap support. This
 			is useful for tracking down temporary early mappings
 			which are not unmapped.
+	early_ptdump[=on]
+			Enable kernel page table dump during boot in current
+			ptdump format. This helps analyze early boot mapping
+			kernel regions.
 
 	earlycon=	[KNL,EARLY] Output early console device and options.
 
diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
index 27e774134e7f..ed30d25ca9de 100644
--- a/arch/arm64/include/asm/ptdump.h
+++ b/arch/arm64/include/asm/ptdump.h
@@ -74,8 +74,10 @@ void __init ptdump_debugfs_register(struct ptdump_info *info, const char *name);
 static inline void ptdump_debugfs_register(struct ptdump_info *info,
 					   const char *name) { }
 #endif /* CONFIG_PTDUMP_DEBUGFS */
+void __init arm64_kernel_pgtable_dump(void);
 #else
 static inline void __init ptdump_init(void) { }
+static inline void __init arm64_kernel_pgtable_dump(void) { }
 static inline void note_page(struct ptdump_state *pt_st, unsigned long addr,
 			     int level, pteval_t val) { }
 static inline void note_page_pte(struct ptdump_state *st, unsigned long addr, pte_t pte) { }
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 0a3812c8e177..86bf7607d304 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -361,6 +361,7 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
 	init_bootcpu_ops();
 	smp_init_cpus();
 	smp_build_mpidr_hash();
+	arm64_kernel_pgtable_dump();
 
 #ifdef CONFIG_ARM64_SW_TTBR0_PAN
 	/*
diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
index c78e6b496dea..1624be5160e4 100644
--- a/arch/arm64/mm/ptdump.c
+++ b/arch/arm64/mm/ptdump.c
@@ -407,6 +407,22 @@ void __init ptdump_init(void)
 	ptdump_initialize();
 }
 
+static bool early_ptdump __initdata;
+
+static int __init parse_early_ptdump(char *arg)
+{
+	if (strcmp(arg, "on") == 0)
+		early_ptdump = true;
+	return 0;
+}
+early_param("early_ptdump", parse_early_ptdump);
+
+void __init arm64_kernel_pgtable_dump(void)
+{
+	if (early_ptdump)
+		ptdump_walk(CONSOLE, &kernel_ptdump_info);
+}
+
 static int __init ptdump_debugfs_init(void)
 {
 	ptdump_debugfs_register(&kernel_ptdump_info, "kernel_page_tables");
-- 
2.25.1