[PATCH V3] powerpc/mm/hash64: memset the pagetable pages on allocation.

[Ram Pai]

On Tue, Feb 13, 2018 at 04:39:33PM +0530, Aneesh Kumar K.V wrote:
> On powerpc we allocate page table pages from slab cache of different sizes. For
> now we have a constructor that zero out the objects when we allocate then for
> the first time. We expect the objects to be zeroed out when we free the the
> object back to slab cache. This happens in the unmap path. For hugetlb pages
> we call huge_pte_get_and_clear to do that. With the current configuration of
> page table size, both pud and pgd level tables get allocated from the same slab
> cache. At the pud level, we use the second half of the table to store the slot
> information. But never clear that when unmapping. When such an freed object get
> allocated at pgd level, we will have part of the page table page not initlaized
> correctly. This result in kernel crash
> 
> Simplify this by calling the object initialization after kmem_cache_alloc
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/book3s/64/pgalloc.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgalloc.h b/arch/powerpc/include/asm/book3s/64/pgalloc.h
> index 53df86d3cfce..e4d154a4d114 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgalloc.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgalloc.h
> @@ -73,10 +73,13 @@ static inline void radix__pgd_free(struct mm_struct *mm, pgd_t *pgd)
> 
>  static inline pgd_t *pgd_alloc(struct mm_struct *mm)
>  {
> +	pgd_t *pgd;
>  	if (radix_enabled())
>  		return radix__pgd_alloc(mm);
> -	return kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE),
> -		pgtable_gfp_flags(mm, GFP_KERNEL));

kmem_cache_zalloc() wont work?

RP

> +	pgd = kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE),
> +			       pgtable_gfp_flags(mm, GFP_KERNEL));
> +	memset(pgd, 0, PGD_TABLE_SIZE);
> +	return pgd;
>  }
> 
>  static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
> -- 
> 2.14.3

-- 
Ram Pai