On Wed, Jun 18, 2025 at 09:42:34AM +0530, Anshuman Khandual wrote:
> Add a new format for printing page table entries.
>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
> 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
Ok, so what's the point of this if you're just printing the number?
Could at least do something like:
%ppte 0xc0ff000|WRITE|DIRTY|PRESENT
no? Otherwise it's a not super useful wrapper around printing pte_val(*pte).
> +
> 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);
> + }
As mentioned elsewhere in the thread, this obviously doesn't work for everything
32-bit, and 64-bit PAE, and all of the weird page table formats we have around.
--
Pedro
