Re: [PATCH -fixes 2/2] riscv: Fix set_huge_pte_at() for NAPOT mappings when a swap entry is set

[Andrew Jones]

On Thu, Sep 28, 2023 at 05:18:46PM +0200, Alexandre Ghiti wrote:
> We used to determine the number of page table entries to set for a NAPOT
> hugepage by using the pte value which actually fails when the pte to set is
> a swap entry.
> 
> So take advantage of a recent fix for arm64 reported in [1] which
> introduces the size of the mapping as an argument of set_huge_pte_at(): we
> can then use this size to compute the number of page table entries to set
> for a NAPOT region.
> 
> Fixes: 82a1a1f3bfb6 ("riscv: mm: support Svnapot in hugetlb page")
> Reported-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> Closes: https://lore.kernel.org/linux-arm-kernel/20230922115804.2043771-1-ryan.roberts@xxxxxxx/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> ---
>  arch/riscv/mm/hugetlbpage.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/riscv/mm/hugetlbpage.c b/arch/riscv/mm/hugetlbpage.c
> index e4a2ace92dbe..b52f0210481f 100644
> --- a/arch/riscv/mm/hugetlbpage.c
> +++ b/arch/riscv/mm/hugetlbpage.c
> @@ -183,15 +183,22 @@ void set_huge_pte_at(struct mm_struct *mm,
>  		     pte_t pte,
>  		     unsigned long sz)
>  {
> +	unsigned long hugepage_shift;
>  	int i, pte_num;
>  
> -	if (!pte_napot(pte)) {
> -		set_pte_at(mm, addr, ptep, pte);
> -		return;
> -	}
> +	if (sz >= PGDIR_SIZE)
> +		hugepage_shift = PGDIR_SHIFT;
> +	else if (sz >= P4D_SIZE)
> +		hugepage_shift = P4D_SHIFT;
> +	else if (sz >= PUD_SIZE)
> +		hugepage_shift = PUD_SHIFT;
> +	else if (sz >= PMD_SIZE)
> +		hugepage_shift = PMD_SHIFT;
> +	else
> +		hugepage_shift = PAGE_SHIFT;
>  
> -	pte_num = napot_pte_num(napot_cont_order(pte));
> -	for (i = 0; i < pte_num; i++, ptep++, addr += PAGE_SIZE)
> +	pte_num = sz >> hugepage_shift;
> +	for (i = 0; i < pte_num; i++, ptep++, addr += (1 << hugepage_shift))
>  		set_pte_at(mm, addr, ptep, pte);
>  }
>

So a 64k napot, for example, will fall into the PAGE_SHIFT arm, but then
we'll calculate 16 for pte_num. Looks good to me.

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>

Thanks,
drew