Re: [PATCH] powerpc/mm/book3s64/hash/4k: Add pmd_same callback for 4K page size

[Hugh Dickins <hughd@google.com>]

On Thu, 6 Jul 2023, Aneesh Kumar K.V wrote:

> With commit 0d940a9b270b ("mm/pgtable: allow pte_offset_map[_lock]() to
> fail") the kernel is now using pmd_same to compare pmd values that are
> pointing to a level 4 page table page. Move the functions out of #ifdef
> CONFIG_TRANSPARENT_HUGEPAGE and add a variant that can work with both 4K
> and 64K page size.
> 
> kernel BUG at arch/powerpc/include/asm/book3s/64/hash-4k.h:141!
> Oops: Exception in kernel mode, sig: 5 [#1]
> LE PAGE_SIZE=4K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> .....
> NIP [c00000000048aee0] __pte_offset_map_lock+0xf0/0x164
> LR [c00000000048ae78] __pte_offset_map_lock+0x88/0x164
> Call Trace:
>  0xc0003f000009a340 (unreliable)
>  __handle_mm_fault+0x1340/0x1980
>  handle_mm_fault+0xbc/0x380
>  __get_user_pages+0x320/0x550
>  get_user_pages_remote+0x13c/0x520
>  get_arg_page+0x80/0x1d0
>  copy_string_kernel+0xc8/0x250
>  kernel_execve+0x11c/0x270
>  run_init_process+0xe4/0x10c
>  kernel_init+0xbc/0x1a0
>  ret_from_kernel_user_thread+0x14/0x1c
> 
> Cc: Hugh Dickins <hughd@google.com>
> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

Acked-by: Hugh Dickins <hughd@google.com>

Thanks for rescuing us so quickly!

> ---
>  arch/powerpc/include/asm/book3s/64/hash-4k.h  | 6 ------
>  arch/powerpc/include/asm/book3s/64/hash-64k.h | 5 -----
>  arch/powerpc/include/asm/book3s/64/hash.h     | 5 +++++
>  3 files changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/hash-4k.h b/arch/powerpc/include/asm/book3s/64/hash-4k.h
> index b6ac4f86c87b..6472b08fa1b0 100644
> --- a/arch/powerpc/include/asm/book3s/64/hash-4k.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash-4k.h
> @@ -136,12 +136,6 @@ static inline int hash__pmd_trans_huge(pmd_t pmd)
>  	return 0;
>  }
>  
> -static inline int hash__pmd_same(pmd_t pmd_a, pmd_t pmd_b)
> -{
> -	BUG();
> -	return 0;
> -}
> -
>  static inline pmd_t hash__pmd_mkhuge(pmd_t pmd)
>  {
>  	BUG();
> diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
> index 338e62fbea0b..0bf6fd0bf42a 100644
> --- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h
> @@ -263,11 +263,6 @@ static inline int hash__pmd_trans_huge(pmd_t pmd)
>  		  (_PAGE_PTE | H_PAGE_THP_HUGE));
>  }
>  
> -static inline int hash__pmd_same(pmd_t pmd_a, pmd_t pmd_b)
> -{
> -	return (((pmd_raw(pmd_a) ^ pmd_raw(pmd_b)) & ~cpu_to_be64(_PAGE_HPTEFLAGS)) == 0);
> -}
> -
>  static inline pmd_t hash__pmd_mkhuge(pmd_t pmd)
>  {
>  	return __pmd(pmd_val(pmd) | (_PAGE_PTE | H_PAGE_THP_HUGE));
> diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
> index 17e7a778c856..d4a19e6547ac 100644
> --- a/arch/powerpc/include/asm/book3s/64/hash.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash.h
> @@ -132,6 +132,11 @@ static inline int get_region_id(unsigned long ea)
>  	return region_id;
>  }
>  
> +static inline int hash__pmd_same(pmd_t pmd_a, pmd_t pmd_b)
> +{
> +	return (((pmd_raw(pmd_a) ^ pmd_raw(pmd_b)) & ~cpu_to_be64(_PAGE_HPTEFLAGS)) == 0);
> +}
> +
>  #define	hash__pmd_bad(pmd)		(pmd_val(pmd) & H_PMD_BAD_BITS)
>  #define	hash__pud_bad(pud)		(pud_val(pud) & H_PUD_BAD_BITS)
>  static inline int hash__p4d_bad(p4d_t p4d)
> -- 
> 2.41.0
> 
>