[RFC V2 0/3] lib/vsprintf: Add support for pgtable entries

[RFC V2 0/3] lib/vsprintf: Add support for pgtable entries

[Anshuman Khandual]

Printing page table entries has been a common requirement both in generic
and platform memory management for various purposes. Hence let's create a
dedicated printk format for such entries which will also help standardize
pgtable printing across different platforms.

Also add a test for this new print format in lib/tests/printf_kunit.c via
existing CONFIG_PRINTF_KUNIT_TEST.

This series applies on v7.1-rc7

This series has been tested on arm64 but built tested on several others
including x86, powerpc, s390, riscv, and mips etc. Although it does not
build on arm32 platform due to existing pgdp_get() concerns.

Changes in V2:

Accommodated most suggestions from Petr Mladek and others

- Moved __print_bad_page_map_pgtable() changes into a separate patch
- Added helper pxd_pointer() for pgtable print format
- Added buffer check via check_pointer()
- Added special_hex_number() for base case printing
- Added static_assert() to ensure acceptable pxd_t size
- Avoided direct dereferences and used pxdp_get() helpers instead
- Improved printf KUNIT tests for all level page table entries

Changes in V1:

https://lore.kernel.org/all/20250618041235.1716143-1-anshuman.khandual@arm.com/

Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-mm@kvack.org

Anshuman Khandual (3):
  lib/vsprintf: Add support for pgtable entries
  kunit: printf: Add test for pgtable entries
  mm: Replace pgtable entry prints with new format

 Documentation/core-api/printk-formats.rst | 19 ++++++++
 lib/tests/printf_kunit.c                  | 57 ++++++++++++++++++++++
 lib/vsprintf.c                            | 58 +++++++++++++++++++++++
 mm/memory.c                               | 15 ++----
 scripts/checkpatch.pl                     |  2 +-
 5 files changed, 140 insertions(+), 11 deletions(-)

-- 
2.30.2

[RFC V2 1/3] lib/vsprintf: Add support for pgtable entries

[Anshuman Khandual]

Add some print formats for pgtable entries at any pgtable level. These new
formats are %pp[g|4|u|m|t][d|e] i.e %ppgd, %pp4d, %ppud, %ppmd, and %ppte.
These currently support both 32 bit and 64 bit pgtable entries that can be
extended up to 128 bit when required.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-doc@vger.kernel.org

 Documentation/core-api/printk-formats.rst | 19 ++++++++
 lib/vsprintf.c                            | 58 +++++++++++++++++++++++
 scripts/checkpatch.pl                     |  2 +-
 3 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index c0b1b6089307..e69f91a9dd9d 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -696,6 +696,25 @@ Rust
 Only intended to be used from Rust code to format ``core::fmt::Arguments``.
 Do *not* use it from C.
 
+Page Table Entry
+----------------
+
+::
+
+        %p[pgd|p4dp|pud|pmd|pte]
+
+Print page table entry at any level.
+
+Passed by reference.
+
+Examples for a 64 bit page table entry, given &(u64)0xc0ffee::
+
+        %ppte   0x0000000000c0ffee
+        %ppmd   0x0000000000c0ffee
+        %ppud   0x0000000000c0ffee
+        %pp4d   0x0000000000c0ffee
+        %ppgd   0x0000000000c0ffee
+
 Thanks
 ======
 
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 9f359b31c8d1..d4ad3048a4db 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -856,6 +856,59 @@ static char *default_pointer(char *buf, char *end, const void *ptr,
 	return ptr_to_id(buf, end, ptr, spec);
 }
 
+static char *pxd_pointer(char *buf, char *end, const void *ptr,
+			 struct printf_spec spec, const char *fmt)
+{
+	if (check_pointer(&buf, end, ptr, spec))
+		return buf;
+
+	if (fmt[1] == 't' && fmt[2] == 'e') {
+		pte_t *pte = (pte_t *)ptr;
+
+		static_assert(sizeof(pte_t) == 4 ||
+			      sizeof(pte_t) == 8,
+			      "pte_t size must be 4 or 8 bytes");
+		return special_hex_number(buf, end, pte_val(ptep_get(pte)), sizeof(pte_t));
+	}
+
+	if (fmt[1] == 'm' && fmt[2] == 'd') {
+		pmd_t *pmd = (pmd_t *)ptr;
+
+		static_assert(sizeof(pmd_t) == 4 ||
+			      sizeof(pmd_t) == 8,
+			      "pmd_t size must be 4 or 8 bytes");
+		return special_hex_number(buf, end, pmd_val(pmdp_get(pmd)), sizeof(pmd_t));
+	}
+
+	if (fmt[1] == 'u' && fmt[2] == 'd') {
+		pud_t *pud = (pud_t *)ptr;
+
+		static_assert(sizeof(pud_t) == 4 ||
+			      sizeof(pud_t) == 8,
+			      "pud_t size must be 4 or 8 bytes");
+		return special_hex_number(buf, end, pud_val(pudp_get(pud)), sizeof(pud_t));
+	}
+
+	if (fmt[1] == '4' && fmt[2] == 'd') {
+		p4d_t *p4d = (p4d_t *)ptr;
+
+		static_assert(sizeof(p4d_t) == 4 ||
+			      sizeof(p4d_t) == 8,
+			      "p4d_t size must be 4 or 8 bytes");
+		return special_hex_number(buf, end, p4d_val(p4dp_get(p4d)), sizeof(p4d_t));
+	}
+
+	if (fmt[1] == 'g' && fmt[2] == 'd') {
+		pgd_t *pgd = (pgd_t *)ptr;
+
+		static_assert(sizeof(pgd_t) == 4 ||
+			      sizeof(pgd_t) == 8,
+			      "pgd_t size must be 4 or 8 bytes");
+		return special_hex_number(buf, end, pgd_val(pgdp_get(pgd)), sizeof(pgd_t));
+	}
+	return default_pointer(buf, end, ptr, spec);
+}
+
 int kptr_restrict __read_mostly;
 
 static noinline_for_stack
@@ -2506,6 +2559,9 @@ early_param("no_hash_pointers", no_hash_pointers_enable);
  *		Without an option prints the full name of the node
  *		f full name
  *		P node name, including a possible unit address
+ * - 'p[g|4|u|m|t|][d|e]' For a page table entry, this prints its
+ *			  contents in a hexadecimal format
+ *
  * - 'x' For printing the address unmodified. Equivalent to "%lx".
  *       Please read the documentation (path below) before using!
  * - '[ku]s' For a BPF/tracing related format specifier, e.g. used out of
@@ -2615,6 +2671,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		default:
 			return error_string(buf, end, "(einval)", spec);
 		}
+	case 'p':
+		return pxd_pointer(buf, end, ptr, spec, fmt);
 	default:
 		return default_pointer(buf, end, ptr, spec);
 	}
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 0492d6afc9a1..f68955858e29 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6975,7 +6975,7 @@ sub process {
 				my $fmt = get_quoted_string($lines[$count - 1], raw_line($count, 0));
 				$fmt =~ s/%%//g;
 
-				while ($fmt =~ /(\%[\*\d\.]*p(\w)(\w*))/g) {
+				while ($fmt =~ /(\%[\*\d\.]*p(\w)(\w*)(pte|pmd|pud|p4d|pgd))/g) {
 					$specifier = $1;
 					$extension = $2;
 					$qualifier = $3;
-- 
2.30.2

[RFC V2 2/3] kunit: printf: Add test for pgtable entries

[Anshuman Khandual]

Add test for new pgtable entry print formats with entry size being 64 bits.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: linux-kernel@vger.kernel.org

 lib/tests/printf_kunit.c | 57 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/lib/tests/printf_kunit.c b/lib/tests/printf_kunit.c
index bb70b9cddadd..850bfc0e3409 100644
--- a/lib/tests/printf_kunit.c
+++ b/lib/tests/printf_kunit.c
@@ -791,6 +791,62 @@ errptr(struct kunit *kunittest)
 #endif
 }
 
+struct pgtable_test {
+	u64 val;
+	const char *name;
+};
+
+static struct pgtable_test pgtable_test_cases[] = {
+	{ .val = 0xc0ffee,		.name = "0x0000000000c0ffee"},
+	{ .val = 0xdeadbeef,		.name = "0x00000000deadbeef"},
+	{ .val = 0xaabbcc,		.name = "0x0000000000aabbcc"},
+	{ .val = 0xcc,			.name = "0x00000000000000cc"},
+	{ .val = 0x1,			.name = "0x0000000000000001"},
+	{ .val = 0x11,			.name = "0x0000000000000011"},
+	{ .val = 0x111,			.name = "0x0000000000000111"},
+	{ .val = 0x10000010001,		.name = "0x0000010000010001"},
+	{ .val = 0xc0ffeec0ffee,	.name = "0x0000c0ffeec0ffee"},
+	{ .val = 0x10000000000,		.name = "0x0000010000000000"},
+	{ .val = 0x11000000000,		.name = "0x0000011000000000"},
+	{ .val = 0x1000000000000001,	.name = "0x1000000000000001"},
+	{ .val = 0x1100000000000010,	.name = "0x1100000000000010"},
+	{ .val = 0x1110000000000100,	.name = "0x1110000000000100"},
+	{ .val = 0xfff000000000ff00,	.name = "0xfff000000000ff00"},
+};
+
+static void
+pgtable_ptr(struct kunit *kunittest)
+{
+	char buf[64];
+	int i;
+
+	if (sizeof(pte_t) != 8)
+		kunit_skip(kunittest, "pte_t size is not 64 bits");
+
+	for (i = 0; i < ARRAY_SIZE(pgtable_test_cases); i++) {
+		pte_t pte = __pte(pgtable_test_cases[i].val);
+		pmd_t pmd = __pmd(pgtable_test_cases[i].val);
+		pud_t pud = __pud(pgtable_test_cases[i].val);
+		p4d_t p4d = __p4d(pgtable_test_cases[i].val);
+		pgd_t pgd = __pgd(pgtable_test_cases[i].val);
+
+		snprintf(buf, sizeof(buf), "%ppte", &pte);
+		KUNIT_EXPECT_STREQ(kunittest, buf, pgtable_test_cases[i].name);
+
+		snprintf(buf, sizeof(buf), "%ppmd", &pmd);
+		KUNIT_EXPECT_STREQ(kunittest, buf, pgtable_test_cases[i].name);
+
+		snprintf(buf, sizeof(buf), "%ppud", &pud);
+		KUNIT_EXPECT_STREQ(kunittest, buf, pgtable_test_cases[i].name);
+
+		snprintf(buf, sizeof(buf), "%pp4d", &p4d);
+		KUNIT_EXPECT_STREQ(kunittest, buf, pgtable_test_cases[i].name);
+
+		snprintf(buf, sizeof(buf), "%ppgd", &pgd);
+		KUNIT_EXPECT_STREQ(kunittest, buf, pgtable_test_cases[i].name);
+	}
+}
+
 static int printf_suite_init(struct kunit_suite *suite)
 {
 	total_tests = 0;
@@ -839,6 +895,7 @@ static struct kunit_case printf_test_cases[] = {
 	KUNIT_CASE(errptr),
 	KUNIT_CASE(fwnode_pointer),
 	KUNIT_CASE(fourcc_pointer),
+	KUNIT_CASE(pgtable_ptr),
 	{}
 };
 
-- 
2.30.2

[RFC V2 3/3] mm: Replace pgtable entry prints with new format

[Anshuman Khandual]

Replace all existing pgtable entry prints with recently added new format in
__print_bad_page_map_pgtable().

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org

 mm/memory.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 86a973119bd4..8a25790f7c24 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -521,7 +521,6 @@ static bool is_bad_page_map_ratelimited(void)
 
 static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long addr)
 {
-	unsigned long long pgdv, p4dv, pudv, pmdv;
 	p4d_t p4d, *p4dp;
 	pud_t pud, *pudp;
 	pmd_t pmd, *pmdp;
@@ -532,34 +531,30 @@ static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long add
 	 * see locking requirements for print_bad_page_map().
 	 */
 	pgdp = pgd_offset(mm, addr);
-	pgdv = pgd_val(*pgdp);
 
 	if (!pgd_present(*pgdp) || pgd_leaf(*pgdp)) {
-		pr_alert("pgd:%08llx\n", pgdv);
+		pr_alert("pgd:%ppgd\n", pgdp);
 		return;
 	}
 
 	p4dp = p4d_offset(pgdp, addr);
 	p4d = p4dp_get(p4dp);
-	p4dv = p4d_val(p4d);
 
 	if (!p4d_present(p4d) || p4d_leaf(p4d)) {
-		pr_alert("pgd:%08llx p4d:%08llx\n", pgdv, p4dv);
+		pr_alert("pgd:%ppgd p4d:%pp4d\n", pgdp, p4dp);
 		return;
 	}
 
 	pudp = pud_offset(p4dp, addr);
 	pud = pudp_get(pudp);
-	pudv = pud_val(pud);
 
 	if (!pud_present(pud) || pud_leaf(pud)) {
-		pr_alert("pgd:%08llx p4d:%08llx pud:%08llx\n", pgdv, p4dv, pudv);
+		pr_alert("pgd:%ppgd p4d:%pp4d pud:%ppud\n", pgdp, p4dp, pudp);
 		return;
 	}
 
 	pmdp = pmd_offset(pudp, addr);
 	pmd = pmdp_get(pmdp);
-	pmdv = pmd_val(pmd);
 
 	/*
 	 * Dumping the PTE would be nice, but it's tricky with CONFIG_HIGHPTE,
@@ -567,8 +562,8 @@ static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long add
 	 * doing another map would be bad. print_bad_page_map() should
 	 * already take care of printing the PTE.
 	 */
-	pr_alert("pgd:%08llx p4d:%08llx pud:%08llx pmd:%08llx\n", pgdv,
-		 p4dv, pudv, pmdv);
+	pr_alert("pgd:%ppgd p4d:%pp4d pud:%ppud pmd:%ppmd\n", pgdp,
+		 p4dp, pudp, pmdp);
 }
 
 /*
-- 
2.30.2

Re: [RFC V2 1/3] lib/vsprintf: Add support for pgtable entries

[Usama Arif]

On Wed, 10 Jun 2026 05:35:43 +0100 Anshuman Khandual <anshuman.khandual@arm.com> wrote:

> Add some print formats for pgtable entries at any pgtable level. These new
> formats are %pp[g|4|u|m|t][d|e] i.e %ppgd, %pp4d, %ppud, %ppmd, and %ppte.
> These currently support both 32 bit and 64 bit pgtable entries that can be
> extended up to 128 bit when required.
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Lorenzo Stoakes <ljs@kernel.org>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Andy Whitcroft <apw@canonical.com>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-doc@vger.kernel.org
> 
>  Documentation/core-api/printk-formats.rst | 19 ++++++++
>  lib/vsprintf.c                            | 58 +++++++++++++++++++++++
>  scripts/checkpatch.pl                     |  2 +-
>  3 files changed, 78 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index c0b1b6089307..e69f91a9dd9d 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -696,6 +696,25 @@ Rust
>  Only intended to be used from Rust code to format ``core::fmt::Arguments``.
>  Do *not* use it from C.
>  
> +Page Table Entry
> +----------------
> +
> +::
> +
> +        %p[pgd|p4dp|pud|pmd|pte]

s/p4dp/p4d to match others


> +
> +Print page table entry at any level.
> +
> +Passed by reference.
> +
> +Examples for a 64 bit page table entry, given &(u64)0xc0ffee::
> +
> +        %ppte   0x0000000000c0ffee
> +        %ppmd   0x0000000000c0ffee
> +        %ppud   0x0000000000c0ffee
> +        %pp4d   0x0000000000c0ffee
> +        %ppgd   0x0000000000c0ffee
> +
>  Thanks
>  ======
>  
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 9f359b31c8d1..d4ad3048a4db 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -856,6 +856,59 @@ static char *default_pointer(char *buf, char *end, const void *ptr,
>  	return ptr_to_id(buf, end, ptr, spec);
>  }
>  
> +static char *pxd_pointer(char *buf, char *end, const void *ptr,
> +			 struct printf_spec spec, const char *fmt)
> +{
> +	if (check_pointer(&buf, end, ptr, spec))
> +		return buf;
> +
> +	if (fmt[1] == 't' && fmt[2] == 'e') {
> +		pte_t *pte = (pte_t *)ptr;
> +
> +		static_assert(sizeof(pte_t) == 4 ||
> +			      sizeof(pte_t) == 8,
> +			      "pte_t size must be 4 or 8 bytes");
> +		return special_hex_number(buf, end, pte_val(ptep_get(pte)), sizeof(pte_t));
> +	}
> +
> +	if (fmt[1] == 'm' && fmt[2] == 'd') {
> +		pmd_t *pmd = (pmd_t *)ptr;
> +
> +		static_assert(sizeof(pmd_t) == 4 ||
> +			      sizeof(pmd_t) == 8,
> +			      "pmd_t size must be 4 or 8 bytes");
> +		return special_hex_number(buf, end, pmd_val(pmdp_get(pmd)), sizeof(pmd_t));
> +	}
> +
> +	if (fmt[1] == 'u' && fmt[2] == 'd') {
> +		pud_t *pud = (pud_t *)ptr;
> +
> +		static_assert(sizeof(pud_t) == 4 ||
> +			      sizeof(pud_t) == 8,
> +			      "pud_t size must be 4 or 8 bytes");
> +		return special_hex_number(buf, end, pud_val(pudp_get(pud)), sizeof(pud_t));
> +	}
> +
> +	if (fmt[1] == '4' && fmt[2] == 'd') {
> +		p4d_t *p4d = (p4d_t *)ptr;
> +
> +		static_assert(sizeof(p4d_t) == 4 ||
> +			      sizeof(p4d_t) == 8,
> +			      "p4d_t size must be 4 or 8 bytes");
> +		return special_hex_number(buf, end, p4d_val(p4dp_get(p4d)), sizeof(p4d_t));
> +	}
> +
> +	if (fmt[1] == 'g' && fmt[2] == 'd') {
> +		pgd_t *pgd = (pgd_t *)ptr;
> +
> +		static_assert(sizeof(pgd_t) == 4 ||
> +			      sizeof(pgd_t) == 8,
> +			      "pgd_t size must be 4 or 8 bytes");
> +		return special_hex_number(buf, end, pgd_val(pgdp_get(pgd)), sizeof(pgd_t));

You mentioned in the coverletter that pgdp_get() is the reason arm32 builds dont work.
Just wanted to check what the issue is?

I had a look at arch/arm/include/asm/pgtable.h and I couldnt understand why
it reads pgdp_get(pgpd) instead of pgdp_get(pgdp)?
   

> +	}
> +	return default_pointer(buf, end, ptr, spec);
> +}
> +
>  int kptr_restrict __read_mostly;
>  
>  static noinline_for_stack
> @@ -2506,6 +2559,9 @@ early_param("no_hash_pointers", no_hash_pointers_enable);
>   *		Without an option prints the full name of the node
>   *		f full name
>   *		P node name, including a possible unit address
> + * - 'p[g|4|u|m|t|][d|e]' For a page table entry, this prints its
> + *			  contents in a hexadecimal format
> + *
>   * - 'x' For printing the address unmodified. Equivalent to "%lx".
>   *       Please read the documentation (path below) before using!
>   * - '[ku]s' For a BPF/tracing related format specifier, e.g. used out of
> @@ -2615,6 +2671,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  		default:
>  			return error_string(buf, end, "(einval)", spec);
>  		}
> +	case 'p':
> +		return pxd_pointer(buf, end, ptr, spec, fmt);
>  	default:
>  		return default_pointer(buf, end, ptr, spec);
>  	}
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 0492d6afc9a1..f68955858e29 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -6975,7 +6975,7 @@ sub process {
>  				my $fmt = get_quoted_string($lines[$count - 1], raw_line($count, 0));
>  				$fmt =~ s/%%//g;
>  
> -				while ($fmt =~ /(\%[\*\d\.]*p(\w)(\w*))/g) {
> +				while ($fmt =~ /(\%[\*\d\.]*p(\w)(\w*)(pte|pmd|pud|p4d|pgd))/g) {
>  					$specifier = $1;
>  					$extension = $2;
>  					$qualifier = $3;
> -- 
> 2.30.2
> 
>