linux-kernel - Re: [PATCH] powerpc/mm: Refactor the floor/ceiling check in hugetlb range freeing functions

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Date:   Wed, 09 Dec 2020 11:59:44 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/mm: Refactor the floor/ceiling check in hugetlb
 range freeing functions

Christophe Leroy <christophe.leroy@...roup.eu> writes:

> All hugetlb range freeing functions have a verification like the following,
> which only differs by the mask used, depending on the page table level.
>
> 	start &= MASK;
> 	if (start < floor)
> 		return;
> 	if (ceiling) {
> 		ceiling &= MASK;
> 		if (! ceiling)
> 			return;
> 		}
> 	if (end - 1 > ceiling - 1)
> 		return;
>
> Refactor that into a helper function which takes the mask as
> an argument, returning true when [start;end[ is not fully
> contained inside [floor;ceiling[
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>

> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/mm/hugetlbpage.c | 56 ++++++++++++-----------------------
>  1 file changed, 19 insertions(+), 37 deletions(-)
>
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index 36c3800769fb..f8d8a4988e15 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -294,6 +294,21 @@ static void hugepd_free(struct mmu_gather *tlb, void *hugepte)
>  static inline void hugepd_free(struct mmu_gather *tlb, void *hugepte) {}
>  #endif
>  
> +/* Return true when the entry to be freed maps more than the area being freed */
> +static bool range_is_outside_limits(unsigned long start, unsigned long end,
> +				    unsigned long floor, unsigned long ceiling,
> +				    unsigned long mask)
> +{
> +	if ((start & mask) < floor)
> +		return true;
> +	if (ceiling) {
> +		ceiling &= mask;
> +		if (!ceiling)
> +			return true;
> +	}
> +	return end - 1 > ceiling - 1;
> +}
> +
>  static void free_hugepd_range(struct mmu_gather *tlb, hugepd_t *hpdp, int pdshift,
>  			      unsigned long start, unsigned long end,
>  			      unsigned long floor, unsigned long ceiling)
> @@ -309,15 +324,7 @@ static void free_hugepd_range(struct mmu_gather *tlb, hugepd_t *hpdp, int pdshif
>  	if (shift > pdshift)
>  		num_hugepd = 1 << (shift - pdshift);
>  
> -	start &= pdmask;
> -	if (start < floor)
> -		return;
> -	if (ceiling) {
> -		ceiling &= pdmask;
> -		if (! ceiling)
> -			return;
> -	}
> -	if (end - 1 > ceiling - 1)
> +	if (range_is_outside_limits(start, end, floor, ceiling, pdmask))
>  		return;
>  
>  	for (i = 0; i < num_hugepd; i++, hpdp++)
> @@ -334,18 +341,9 @@ static void hugetlb_free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
>  				   unsigned long addr, unsigned long end,
>  				   unsigned long floor, unsigned long ceiling)
>  {
> -	unsigned long start = addr;
>  	pgtable_t token = pmd_pgtable(*pmd);
>  
> -	start &= PMD_MASK;
> -	if (start < floor)
> -		return;
> -	if (ceiling) {
> -		ceiling &= PMD_MASK;
> -		if (!ceiling)
> -			return;
> -	}
> -	if (end - 1 > ceiling - 1)
> +	if (range_is_outside_limits(addr, end, floor, ceiling, PMD_MASK))
>  		return;
>  
>  	pmd_clear(pmd);
> @@ -395,15 +393,7 @@ static void hugetlb_free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
>  				  addr, next, floor, ceiling);
>  	} while (addr = next, addr != end);
>  
> -	start &= PUD_MASK;
> -	if (start < floor)
> -		return;
> -	if (ceiling) {
> -		ceiling &= PUD_MASK;
> -		if (!ceiling)
> -			return;
> -	}
> -	if (end - 1 > ceiling - 1)
> +	if (range_is_outside_limits(start, end, floor, ceiling, PUD_MASK))
>  		return;
>  
>  	pmd = pmd_offset(pud, start);
> @@ -446,15 +436,7 @@ static void hugetlb_free_pud_range(struct mmu_gather *tlb, p4d_t *p4d,
>  		}
>  	} while (addr = next, addr != end);
>  
> -	start &= PGDIR_MASK;
> -	if (start < floor)
> -		return;
> -	if (ceiling) {
> -		ceiling &= PGDIR_MASK;
> -		if (!ceiling)
> -			return;
> -	}
> -	if (end - 1 > ceiling - 1)
> +	if (range_is_outside_limits(start, end, floor, ceiling, PGDIR_MASK))
>  		return;
>  
>  	pud = pud_offset(p4d, start);
> -- 
> 2.25.0