linux-kernel - [RFC 1/2] lib/vsprintf: Add support for pte

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Message-Id: <20250618041235.1716143-2-anshuman.khandual@arm.com>
Date: Wed, 18 Jun 2025 09:42:34 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: linux-mm@...ck.org
Cc: Anshuman Khandual <anshuman.khandual@....com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: [RFC 1/2] lib/vsprintf: Add support for pte_t

Add a new format for printing page table entries.

Cc: Petr Mladek <pmladek@...e.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Jonathan Corbet <corbet@....net>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 Documentation/core-api/printk-formats.rst | 14 ++++++++++++++
 lib/vsprintf.c                            | 20 ++++++++++++++++++++
 mm/memory.c                               |  5 ++---
 scripts/checkpatch.pl                     |  2 +-
 4 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 4b7f3646ec6ce..75a110b059ee1 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -689,6 +689,20 @@ Rust
 Only intended to be used from Rust code to format ``core::fmt::Arguments``.
 Do *not* use it from C.
 
+Page Table Entry
+----------------
+
+::
+        %ppte
+
+Print standard page table entry pte_t.
+
+Passed by reference.
+
+Examples for a 64 bit page table entry, given &(u64)0xc0ffee::
+
+        %ppte   0x00c0ffee
+
 Thanks
 ======
 
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3d85800757aa5..005490202ffb5 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2433,6 +2433,9 @@ 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
+ * - 'pte'	For a 64 bit page table entry, this prints its contents in
+ *              a hexa decimal 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
@@ -2542,6 +2545,23 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		default:
 			return error_string(buf, end, "(einval)", spec);
 		}
+	case 'p':
+		if (fmt[1] == 't' && fmt[2] == 'e') {
+			pte_t *pte = (pte_t *)ptr;
+
+			spec.field_width = 10;
+			spec.precision = 8;
+			spec.base = 16;
+			spec.flags = SPECIAL | SMALL | ZEROPAD;
+			if (sizeof(pte_t) == sizeof(u64)) {
+				u64 val = pte_val(*pte);
+
+				return number(buf, end, val, spec);
+			}
+			WARN_ONCE(1, "Non standard pte_t\n");
+			return error_string(buf, end, "(einval)", spec);
+		}
+		fallthrough;
 	default:
 		return default_pointer(buf, end, ptr, spec);
 	}
diff --git a/mm/memory.c b/mm/memory.c
index 8eba595056fe3..c9a057b371eae 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -522,9 +522,8 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
 	mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
 	index = linear_page_index(vma, addr);
 
-	pr_alert("BUG: Bad page map in process %s  pte:%08llx pmd:%08llx\n",
-		 current->comm,
-		 (long long)pte_val(pte), (long long)pmd_val(*pmd));
+	pr_alert("BUG: Bad page map in process %s  pte:%ppte pmd:%ppte\n",
+		 current->comm, &pte, pmd);
 	if (page)
 		dump_page(page, "bad pte");
 	pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n",
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 664f7b7a622c2..fb8abc5dbfb8e 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6906,7 +6906,7 @@ 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*)(\te))/g) {
 					$specifier = $1;
 					$extension = $2;
 					$qualifier = $3;
-- 
2.30.2