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

[Christophe Leroy]

Le 31/07/2024 à 09:56, Ritesh Harjani (IBM) a écrit :
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> 
> 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) <ritesh.list at gmail.com>
> ---
>   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 ?

>                  /*
>                   * Pick a size for the linear mapping. Currently, we only
>                   * support 16M, 1M and 4K which is the default
> --
> 2.45.2
>