[PATCH 0/3] arm64/ptdump: Add cmdline 'early_ptdump'

[PATCH 0/3] arm64/ptdump: Add cmdline 'early_ptdump'

[Anshuman Khandual]

Enable early kernel page table dump for debug purpose when required through
a new kernel command line option 'early_ptdump'. But first this reorganizes
ptdump_init() separating out the debugfs creation, so that it can be called
early on in setup_arch(). This also adds kernel dmesg console print support
for existing pt_dump_seq_[printf|puts]() helpers.

This series applies on v6.17-rc5

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-efi@vger.kernel.org

Changes in V1:

- Dropped ARM64_PTDUMP_CONSOLE and instead enabled cmdline 'early_ptdump'

Changes in RFC:

https://lore.kernel.org/all/20250818091436.938517-1-anshuman.khandual@arm.com/

Anshuman Khandual (3):
  arm64/ptdump: Re-organize ptdump_init()
  arm64/ptdump: Enable console output in pt_dump_seq_[printf|puts]()
  arm64/ptdump: Add 'early_ptdump' kernel command line option

 .../admin-guide/kernel-parameters.txt         |  4 ++
 arch/arm64/include/asm/ptdump.h               |  4 ++
 arch/arm64/kernel/setup.c                     |  3 ++
 arch/arm64/mm/ptdump.c                        | 51 +++++++++++++++----
 drivers/firmware/efi/arm-runtime.c            |  4 +-
 5 files changed, 53 insertions(+), 13 deletions(-)

-- 
2.25.1

[PATCH 1/3] arm64/ptdump: Re-organize ptdump_init()

[Anshuman Khandual]

Split ptdump_debugfs_register() from ptdump_init() which there after can be
called early on during the boot and also enable dump kernel page table when
required. While here rename ptdump_init() as ptdump_debugfs_init() to avoid
name space collision.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-efi@vger.kernel.org
Suggested-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/arm64/include/asm/ptdump.h    | 2 ++
 arch/arm64/kernel/setup.c          | 2 ++
 arch/arm64/mm/ptdump.c             | 8 ++++++--
 drivers/firmware/efi/arm-runtime.c | 4 ++--
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
index fded5358641f..27e774134e7f 100644
--- a/arch/arm64/include/asm/ptdump.h
+++ b/arch/arm64/include/asm/ptdump.h
@@ -57,6 +57,7 @@ struct ptdump_pg_state {
 	unsigned long uxn_pages;
 };
 
+void __init ptdump_init(void);
 void ptdump_walk(struct seq_file *s, struct ptdump_info *info);
 void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
 	       pteval_t val);
@@ -74,6 +75,7 @@ static inline void ptdump_debugfs_register(struct ptdump_info *info,
 					   const char *name) { }
 #endif /* CONFIG_PTDUMP_DEBUGFS */
 #else
+static inline void __init ptdump_init(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 77c7926a4df6..0a3812c8e177 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -43,6 +43,7 @@
 #include <asm/cpu_ops.h>
 #include <asm/kasan.h>
 #include <asm/numa.h>
+#include <asm/ptdump.h>
 #include <asm/rsi.h>
 #include <asm/scs.h>
 #include <asm/sections.h>
@@ -332,6 +333,7 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
 	arm64_memblock_init();
 
 	paging_init();
+	ptdump_init();
 
 	acpi_table_upgrade();
 
diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
index 421a5de806c6..7c42be62898b 100644
--- a/arch/arm64/mm/ptdump.c
+++ b/arch/arm64/mm/ptdump.c
@@ -367,7 +367,7 @@ bool ptdump_check_wx(void)
 	}
 }
 
-static int __init ptdump_init(void)
+void __init ptdump_init(void)
 {
 	u64 page_offset = _PAGE_OFFSET(vabits_actual);
 	u64 vmemmap_start = (u64)virt_to_page((void *)page_offset);
@@ -396,7 +396,11 @@ static int __init ptdump_init(void)
 	kernel_ptdump_info.base_addr = page_offset;
 
 	ptdump_initialize();
+}
+
+static int __init ptdump_debugfs_init(void)
+{
 	ptdump_debugfs_register(&kernel_ptdump_info, "kernel_page_tables");
 	return 0;
 }
-device_initcall(ptdump_init);
+device_initcall(ptdump_debugfs_init);
diff --git a/drivers/firmware/efi/arm-runtime.c b/drivers/firmware/efi/arm-runtime.c
index 83092d93f36a..3c84e84dc6ea 100644
--- a/drivers/firmware/efi/arm-runtime.c
+++ b/drivers/firmware/efi/arm-runtime.c
@@ -38,14 +38,14 @@ static struct ptdump_info efi_ptdump_info = {
 	.base_addr	= 0,
 };
 
-static int __init ptdump_init(void)
+static int __init ptdump_debugfs_init(void)
 {
 	if (efi_enabled(EFI_RUNTIME_SERVICES))
 		ptdump_debugfs_register(&efi_ptdump_info, "efi_page_tables");
 
 	return 0;
 }
-device_initcall(ptdump_init);
+device_initcall(ptdump_debugfs_init);
 
 #endif
 
-- 
2.25.1

[PATCH 2/3] arm64/ptdump: Enable console output in pt_dump_seq_[printf|puts]()

[Anshuman Khandual]

Enable console output in pt_dump_seq_[printf|puts]() in order to dump early
kernel page tables when required. CONFIG_DEBUG_WX enabled ptdump_check_wx()
already sets seq file as NULL to avoid all output. Hence let's introduce a
special sentinel named CONSOLE as ((struct seq_file *)-1) which can be used
to identify kernel console output request for early kernel page table dump.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/arm64/mm/ptdump.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
index 7c42be62898b..c78e6b496dea 100644
--- a/arch/arm64/mm/ptdump.c
+++ b/arch/arm64/mm/ptdump.c
@@ -25,17 +25,26 @@
 #include <asm/pgtable-hwdef.h>
 #include <asm/ptdump.h>
 
-
-#define pt_dump_seq_printf(m, fmt, args...)	\
-({						\
-	if (m)					\
-		seq_printf(m, fmt, ##args);	\
+#define CONSOLE ((struct seq_file *)-1)
+
+#define pt_dump_seq_printf(m, fmt, args...)		\
+({							\
+	if (m) {					\
+		if (m == CONSOLE)			\
+			pr_cont(fmt, ##args);		\
+		else					\
+			seq_printf(m, fmt, ##args);	\
+	}						\
 })
 
-#define pt_dump_seq_puts(m, fmt)	\
-({					\
-	if (m)				\
-		seq_printf(m, fmt);	\
+#define pt_dump_seq_puts(m, fmt)		\
+({						\
+	if (m)	{				\
+		if (m == CONSOLE)		\
+			pr_cont(fmt);		\
+		else				\
+			seq_printf(m, fmt);	\
+	}					\
 })
 
 static const struct ptdump_prot_bits pte_bits[] = {
-- 
2.25.1

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

[Anshuman Khandual]

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@lwn.net>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Suggested-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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

Re: [PATCH 0/3] arm64/ptdump: Add cmdline 'early_ptdump'

[Will Deacon]

On Wed, Sep 10, 2025 at 03:16:20PM +0530, Anshuman Khandual wrote:
> Enable early kernel page table dump for debug purpose when required through
> a new kernel command line option 'early_ptdump'. But first this reorganizes
> ptdump_init() separating out the debugfs creation, so that it can be called
> early on in setup_arch(). This also adds kernel dmesg console print support
> for existing pt_dump_seq_[printf|puts]() helpers.
> 
> This series applies on v6.17-rc5
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-efi@vger.kernel.org

I'm really not convinced this is particularly useful and I've certainly
never felt the need to have something like it. If you're debugging really
early page-table issues, why you want to rely on all the ptdump
infrastructure to get logs out?

On the other hand, if people do find this useful, then I think it should
be implemented in the core code rather than done behind its back in the
arch code.

Will