Subject: Re: [RFC v1 10/10] book3s64/hash: Disable kfence if not early init

From: Ritesh Harjani (IBM) <[email-masked]>
Date: Thu, 05 Sep 2024 00:14:31 +0530

Christophe Leroy <[email-masked]> writes:

> Le 31/07/2024 à 09:56, Ritesh Harjani (IBM) a écrit :
>> [Vous ne recevez pas souvent de courriers de [email-masked]. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>> 
>> Enable kfence on book3s64 hash only when early init is enabled.
>> This is because, kfence could cause the kernel linear map to be mapped
>> at PAGE_SIZE level instead of 16M (which I guess we don't want).
>> 
>> Also currently there is no way to -
>> 1. Make multiple page size entries for the SLB used for kernel linear
>>     map.
>> 2. No easy way of getting the hash slot details after the page table
>>     mapping for kernel linear setup. So even if kfence allocate the
>>     pool in late init, we won't be able to get the hash slot details in
>>     kfence linear map.
>> 
>> Thus this patch disables kfence on hash if kfence early init is not
>> enabled.
>> 
>> Signed-off-by: Ritesh Harjani (IBM) <[email-masked]>
>> ---
>>   arch/powerpc/mm/book3s64/hash_utils.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
>> index c66b9921fc7d..759dbcbf1483 100644
>> --- a/arch/powerpc/mm/book3s64/hash_utils.c
>> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
>> @@ -410,6 +410,8 @@ static phys_addr_t kfence_pool;
>> 
>>   static inline void hash_kfence_alloc_pool(void)
>>   {
>> +       if (!kfence_early_init)
>> +               goto err;
>> 
>>          // allocate linear map for kfence within RMA region
>>          linear_map_kf_hash_count = KFENCE_POOL_SIZE >> PAGE_SHIFT;
>> @@ -1074,7 +1076,8 @@ static void __init htab_init_page_sizes(void)
>>          bool aligned = true;
>>          init_hpte_page_sizes();
>> 
>> -       if (!debug_pagealloc_enabled_or_kfence()) {
>> +       if (!debug_pagealloc_enabled() &&
>> +           !(IS_ENABLED(CONFIG_KFENCE) && kfence_early_init)) {
>
> Looks complex, can we do simpler ?
>

Yes, kfence_early_init anyway needs clean up. Will make it simpler.

Thanks for the review!

-ritesh