[PATCH 3/3] powerpc: mm: support page table check

[Rohan McLure]

> On 12 Sep 2022, at 4:11 pm, Christophe Leroy <christophe.leroy at csgroup.eu> wrote:
> 
> 
> 
> Le 12/09/2022 à 03:47, Rohan McLure a écrit :
>> On creation and clearing of a page table mapping, instrument such calls
>> by invoking page_table_check_pte_set and page_table_check_pte_clear
>> respectively. These calls serve as a sanity check against illegal
>> mappings.
>> 
>> Enable ARCH_SUPPORTS_PAGE_TABLE_CHECK for all ppc64, and 32-bit
>> platforms implementing Book3S.
> 
> Why only book3s on 32 bits ?

Sorry. I failed to update that commit message. This patch instead supports,
page table checks on all platforms, but I began writing this patch series to
target just Book3S, and then updated it to include all platforms. The only
barrier to doing so was the need for the pud_pfn and
page_table_check_pud_{clear,set} bloat.

>> +++ b/arch/powerpc/include/asm/pgtable.h
>> @@ -166,7 +166,11 @@ static inline int pud_pfn(pud_t pud)
>>  	 * check so this should never be used. If it grows another user we
>>  	 * want to know about it.
>>  	 */
>> +#ifndef CONFIG_PAGE_TABLE_CHECK
>>  	BUILD_BUG();
>> +#else
>> +	BUG();
>> +#endif
> 
> Awfull.

Quite right. I suspect you can infer the intention here, which is to enforce
that this dead code must not be included anywhere in generic code, but rather
be gated by pud_devmap. I will relax this to a WARN().