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

[Anshuman Khandual <anshuman.khandual@arm.com>]

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