Re: [PATCH V2] mm: Standardize printing for pgtable entries

["David Hildenbrand (Arm)" <david@kernel.org>]

On 7/8/26 10:43, Anshuman Khandual wrote:
> On 08/07/26 1:31 PM, David Hildenbrand (Arm) wrote:
>> On 7/8/26 05:28, Anshuman Khandual wrote:
>>> From: "David Hildenbrand (Arm)" <david@kernel.org>
>>>
>>> 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@linux-foundation.org>
>>> Cc: linux-mm@kvack.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>>
>> I still think you should add your
>>
>> Co-developed-by :)
> 
> OK - will add.
> 
>>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>>> ---
>>> This patch applies on v7.2-rc2
>>>
>>> Changes in V2:
>>>
>>> - Dropped space after ":" during print per Matthew
>>> - Dropped CONFIG_CPU_BIG_ENDIAN per David
>>>
>>> Changes in V1:
>>>
>>> https://lore.kernel.org/all/20260707041703.658021-1-anshuman.khandual@arm.com/
>>>
>>>  mm/memory.c | 98 ++++++++++++++++++++++++++++++++++++++++-------------
>>>  1 file changed, 75 insertions(+), 23 deletions(-)
>>>
>>
>> In general, LGTM (I wrote of it, lol)
>>
>>> diff --git a/mm/memory.c b/mm/memory.c
>>> index ff338c2abe92..a2b63af82792 100644
>>> --- a/mm/memory.c
>>> +++ b/mm/memory.c
>>> @@ -519,9 +519,48 @@ static bool is_bad_page_map_ratelimited(void)
>>>  	return false;
>>>  }
>>>  
>>> +#define PTVAL_STR_MAX	(32 + 1) /* Max 128-bit value in hex + NUL */
>>
>> We could reduce the stack space for !__SIZEOF_INT128__, but not sure if worth it.
>>
>> __print_bad_page_map_pgtable() will currently consume 132 bytes for strings,
>> guess that's still tolerable.
>>
> 
> That's a good point. Are you looking for something like the following
> where stack space can be saved if __SIZEOF_INT128__ is not supported.
> 
> #if defined(__SIZEOF_INT128__)
> #define PTVAL_STR_MAX   (32 + 1) /* Max 128-bit value in hex + NUL */
> #else
> #define PTVAL_STR_MAX   (16 + 1) /* Max 64-bit value in hex + NUL */
> #endif

Yes, something like that. Again, not sure if we need that right now, but it sure
looks logical to try reducing stack usage if easily possible.

-- 
Cheers,

David