Re: [PATCH] mm: Standardize printing for pgtable entries

[David Hildenbrand (Arm)]

On 7/7/26 06:17, Anshuman Khandual wrote:
> From: "David Hildenbrand (Arm)" <david@xxxxxxxxxx>
> 
> Bad page map reporting currently stores page table entry values in an
> unsigned long long and prints them with fixed 64-bit-oriented format
> strings. This is inconsistent across call sites and does not work well for
> architectures where page table entry values are not naturally represented
> as 64-bit values, such as 32-bit or 128-bit entries.
> 
> Introduce a common helper to convert raw page table entry values into a
> fixed-width hexadecimal string based on the actual entry size. Use it for
> bad page map reporting and for dumping the page table walk in
> __print_bad_page_map_pgtable().
> 
> Pass page table entry values to the reporting path as raw bytes together
> with their size, instead of forcing them through an unsigned long long.
> It keeps the printed output consistent and avoids truncation or misleading
> formatting for non-64-bit page table entries.
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

You should add a Co-developed-by here :)

> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---

[...]

> +
> +static void ptval_bytes_to_hex_str(char *buf, size_t buf_size, const void *entry, size_t entry_size)
> +{
> +	if (WARN_ON_ONCE(buf_size < entry_size * 2 + 1)) {
> +		snprintf(buf, buf_size, "overflow");
> +		return;
> +	}
> +
> +	switch (entry_size) {
> +	case sizeof(u32):
> +		snprintf(buf, buf_size, "%08x", *(const u32 *)entry);
> +		break;
> +	case sizeof(u64):
> +		snprintf(buf, buf_size, "%016llx", *(const u64 *)entry);
> +		break;
> +#if defined(__SIZEOF_INT128__)
> +	case sizeof(u128): {
> +		const u64 *val = entry;
> +
> +		if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
> +			snprintf(buf, buf_size, "%016llx%016llx", val[0], val[1]);
> +		else
> +			snprintf(buf, buf_size, "%016llx%016llx", val[1], val[0]);
> +		break;

As discussed, can we simplify that by casting to (u128) and then shifting the
values into place?

-- 
Cheers,

David