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

[Julien Grall <julien.grall@xxxxxxx>]

On 12/05/16 12:30, Peng Fan wrote:
> 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?
Yes.

> For the commit log, I would like to change to this:
> "
> To ARM64, "frametable_size >> SECOND_SHIFT" means the number
On ARM64,

s/means/computes/


> of second level entries, not the number of second level pages.
>
> "ROUNDUP(frametable_size, FIRST_SIZE) >> FIRST_SHIFT" which means
s/means/computes/

> the number of the first level entries(the number of second level pages),
missing space after "entries"

> is the correct one that should be used.
> "
Regards,

--
Julien Grall

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