Re: [PATCH] xen/arm: p2m_set_entry duplicate calculation.

[Julien Grall <julien@xxxxxxx>]

Hi,

On 21/04/2022 16:17, Paran Lee wrote:
> It doesn't seem necessary to do that calculation of order shift again.
I think we need to weight that against increasing the number of local 
variables that do pretty much the same.
This is pretty much done to a matter of taste here. IMHO, the original 
version is better but I see Stefano reviewed it so I will not argue 
against it.
That said, given you already sent a few patches, can you explain why you 
are doing this? Is this optimization purpose? Is it clean-up?
> Signed-off-by: Paran Lee <p4ranlee@xxxxxxxxx>
> ---
>   xen/arch/arm/p2m.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 1d1059f7d2..533afc830a 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1092,7 +1092,7 @@ int p2m_set_entry(struct p2m_domain *p2m,
>       while ( nr )
>       {
>           unsigned long mask;
> -        unsigned long order;
> +        unsigned long order, pages;
>   
>           /*
>            * Don't take into account the MFN when removing mapping (i.e
> @@ -1118,11 +1118,12 @@ int p2m_set_entry(struct p2m_domain *p2m,
>           if ( rc )
>               break;
>   
> -        sgfn = gfn_add(sgfn, (1 << order));
> +        pages = 1 << order;
Please take the opportunity to switch to 1UL.

> +        sgfn = gfn_add(sgfn, pages);
>           if ( !mfn_eq(smfn, INVALID_MFN) )
> -           smfn = mfn_add(smfn, (1 << order));
> +           smfn = mfn_add(smfn, pages);
>   
> -        nr -= (1 << order);
> +        nr -= pages;
>       }
>   
>       return rc;
Cheers,

--
Julien Grall