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

[Peng Fan <van.freenix@xxxxxxxxx>]

Hi Julien,

On Thu, May 12, 2016 at 11:48:30AM +0100, Julien Grall wrote:
>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;

Agree.

>
>This would also benefit a comment to explain that second level of page table
>are populating.

Do you mean I need to add a comment for the upper code?

For the commit log, I would like to change to this:
"
To ARM64, "frametable_size >> SECOND_SHIFT" means the number
of second level entries, not the number of second level pages.

"ROUNDUP(frametable_size, FIRST_SIZE) >> FIRST_SHIFT" which means
the number of the first level entries(the number of second level pages),
is the correct one that should be used.
"
How do you think?

Thanks,
Peng.
>
>>      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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