Re: [Xen-devel] [PATCH] xen/arm: mm: fix nr_second calculation in setup_frametable_mappings

[Julien Grall <julien.grall@xxxxxxx>]

Hi Peng,

On 12/05/16 07:36, Peng Fan wrote:
> To ARM64, "frametable_size >> SECOND_SHIFT" means the number
> of second level entries, not the number of second level pages.
>
> "DIV_ROUND_UP(frametable_size >> SECOND_SHIFT, LPAE_ENTRIES)"
> is the correct way to calculate the second level pages needed
> for frametable mapping.
Good catch!

> Signed-off-by: Peng Fan <van.freenix@xxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> ---
>   xen/arch/arm/mm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 0a4f845..7c7f8e9 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -767,7 +767,7 @@ void __init setup_frametable_mappings(paddr_t ps, paddr_t 
> pe)
>       base_mfn = alloc_boot_pages(frametable_size >> PAGE_SHIFT, 32<<(20-12));
>
>   #ifdef CONFIG_ARM_64
> -    nr_second = frametable_size >> SECOND_SHIFT;
> +    nr_second = DIV_ROUND_UP(frametable_size >> SECOND_SHIFT, LPAE_ENTRIES);

I think the following would be clearer:

ROUNDUP(frametable_size, FIRST_SIZE) >> FIRST_SHIFT;

This would also benefit a comment to explain that second level of page 
table are populating.
>       second_base = alloc_boot_pages(nr_second, 1);
>       second = mfn_to_virt(second_base);
>       for ( i = 0; i < nr_second; i++ )
Regards,

--
Julien Grall

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