Re: [RFC V2 1/3] lib/vsprintf: Add support for pgtable entries
From: Anshuman Khandual
Date: Thu Jun 11 2026 - 01:26:28 EST
On 10/06/26 4:43 PM, Usama Arif wrote:
> On Wed, 10 Jun 2026 05:35:43 +0100 Anshuman Khandual <anshuman.khandual@xxxxxxx> 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@xxxxxxx>
>> ---
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: David Hildenbrand <david@xxxxxxxxxx>
>> Cc: Lorenzo Stoakes <ljs@xxxxxxxxxx>
>> Cc: Petr Mladek <pmladek@xxxxxxxx>
>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> Cc: Jonathan Corbet <corbet@xxxxxxx>
>> Cc: Andy Whitcroft <apw@xxxxxxxxxxxxx>
>> Cc: linux-mm@xxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> Cc: linux-doc@xxxxxxxxxxxxxxx
>>
>> 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
Will fix.
>
>
>> +
>> +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)?
Right - that's a typo.
Following arm32 pgtable header change enables the build.
diff --git a/arch/arm/include/asm/pgtable-2level-types.h b/arch/arm/include/asm/pgtable-2level-types.h
index 650e793f4142..3f1d52402129 100644
--- a/arch/arm/include/asm/pgtable-2level-types.h
+++ b/arch/arm/include/asm/pgtable-2level-types.h
@@ -31,6 +31,7 @@ typedef struct { pteval_t pgprot; } pgprot_t;
#define __pte(x) ((pte_t) { (x) } )
#define __pmd(x) ((pmd_t) { (x) } )
#define __pgprot(x) ((pgprot_t) { (x) } )
+#define __pgd(x) ((pgd_t) { { (x), 0 } })
#else
/*
@@ -49,6 +50,7 @@ typedef pteval_t pgprot_t;
#define __pte(x) (x)
#define __pmd(x) (x)
#define __pgprot(x) (x)
+#define __pgd(x) { (x), 0 }
#endif /* STRICT_MM_TYPECHECKS */
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index 982795cf4563..349e1f819385 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -141,7 +141,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
-#define pgdp_get(pgpd) READ_ONCE(*pgdp)
+#define pgdp_get(pgdp) READ_ONCE(*pgdp)
#define pud_page(pud) pmd_page(__pmd(pud_val(pud)))
#define pud_write(pud) pmd_write(__pmd(pud_val(pud)))
>
>
>> + }
>> + 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
>>
>>