[RFC v1 01/10] book3s64/hash: Remove kfence support temporarily

[Christophe Leroy]

Le 31/07/2024 à 09:56, Ritesh Harjani (IBM) a écrit :
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> 
> Kfence on book3s Hash on pseries is anyways broken. It fails to boot
> due to RMA size limitation. That is because, kfence with Hash uses
> debug_pagealloc infrastructure. debug_pagealloc allocates linear map
> for entire dram size instead of just kfence relevant objects.
> This means for 16TB of DRAM it will require (16TB >> PAGE_SHIFT)
> which is 256MB which is half of RMA region on P8.
> crash kernel reserves 256MB and we also need 2048 * 16KB * 3 for
> emergency stack and some more for paca allocations.
> That means there is not enough memory for reserving the full linear map
> in the RMA region, if the DRAM size is too big (>=16TB)
> (The issue is seen above 8TB with crash kernel 256 MB reservation).
> 
> Now Kfence does not require linear memory map for entire DRAM.
> It only needs for kfence objects. So this patch temporarily removes the
> kfence functionality since debug_pagealloc code needs some refactoring.
> We will bring in kfence on Hash support in later patches.
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list at gmail.com>
> ---
>   arch/powerpc/include/asm/kfence.h     |  5 +++++
>   arch/powerpc/mm/book3s64/hash_utils.c | 16 +++++++++++-----
>   2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/kfence.h b/arch/powerpc/include/asm/kfence.h
> index fab124ada1c7..f3a9476a71b3 100644
> --- a/arch/powerpc/include/asm/kfence.h
> +++ b/arch/powerpc/include/asm/kfence.h
> @@ -10,6 +10,7 @@
> 
>   #include <linux/mm.h>
>   #include <asm/pgtable.h>
> +#include <asm/mmu.h>
> 
>   #ifdef CONFIG_PPC64_ELF_ABI_V1
>   #define ARCH_FUNC_PREFIX "."
> @@ -25,6 +26,10 @@ static inline void disable_kfence(void)
> 
>   static inline bool arch_kfence_init_pool(void)
>   {
> +#ifdef CONFIG_PPC64
> +       if (!radix_enabled())
> +               return false;
> +#endif

Avoid #ifdefs whenever possible. Here you can do:

	if (IS_ENABLED(CONFIG_PPC64) && !radix_enabled())
		return false;

>          return !kfence_disabled;
>   }
>   #endif
> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
> index 01c3b4b65241..1a1b50735fa0 100644
> --- a/arch/powerpc/mm/book3s64/hash_utils.c
> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
> @@ -431,7 +431,7 @@ int htab_bolt_mapping(unsigned long vstart, unsigned long vend,
>                          break;
> 
>                  cond_resched();
> -               if (debug_pagealloc_enabled_or_kfence() &&
> +               if (debug_pagealloc_enabled() &&
>                          (paddr >> PAGE_SHIFT) < linear_map_hash_count)
>                          linear_map_hash_slots[paddr >> PAGE_SHIFT] = ret | 0x80;
>          }
> @@ -814,7 +814,7 @@ 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()) {
>                  /*
>                   * Pick a size for the linear mapping. Currently, we only
>                   * support 16M, 1M and 4K which is the default
> @@ -1134,7 +1134,7 @@ static void __init htab_initialize(void)
> 
>          prot = pgprot_val(PAGE_KERNEL);
> 
> -       if (debug_pagealloc_enabled_or_kfence()) {
> +       if (debug_pagealloc_enabled()) {
>                  linear_map_hash_count = memblock_end_of_DRAM() >> PAGE_SHIFT;
>                  linear_map_hash_slots = memblock_alloc_try_nid(
>                                  linear_map_hash_count, 1, MEMBLOCK_LOW_LIMIT,
> @@ -2117,7 +2117,7 @@ void hpt_do_stress(unsigned long ea, unsigned long hpte_group)
>          }
>   }
> 
> -#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KFENCE)
> +#if defined(CONFIG_DEBUG_PAGEALLOC)

Use #ifdef

>   static DEFINE_RAW_SPINLOCK(linear_map_hash_lock);
> 
>   static void kernel_map_linear_page(unsigned long vaddr, unsigned long lmi)
> @@ -2191,7 +2191,13 @@ int hash__kernel_map_pages(struct page *page, int numpages, int enable)
>          local_irq_restore(flags);
>          return 0;
>   }
> -#endif /* CONFIG_DEBUG_PAGEALLOC || CONFIG_KFENCE */
> +#else /* CONFIG_DEBUG_PAGEALLOC */
> +int hash__kernel_map_pages(struct page *page, int numpages,
> +                                        int enable)
> +{
> +       return 0;
> +}
> +#endif /* CONFIG_DEBUG_PAGEALLOC */
> 
>   void hash__setup_initial_memory_limit(phys_addr_t first_memblock_base,
>                                  phys_addr_t first_memblock_size)
> --
> 2.45.2
>