Re: [Xen-devel] [RFC XEN PATCH v3 01/39] x86_64/mm: fix the PDX group check in mem_hotadd_check()

[Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>]

On Mon, 2017-09-11 at 12:37 +0800, Haozhong Zhang wrote:
> The current check refuses the hot-plugged memory that falls in one
> unused PDX group, which should be allowed.

Looks reasonable to me. The only thing I can think of is you can double
check if the following find_next_zero_bit/find_next_bit will still
work. 

Chao
> 
> Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> ---
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
>  xen/arch/x86/x86_64/mm.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
> index 11746730b4..6c5221f90c 100644
> --- a/xen/arch/x86/x86_64/mm.c
> +++ b/xen/arch/x86/x86_64/mm.c
> @@ -1296,12 +1296,8 @@ static int mem_hotadd_check(unsigned long spfn,
> unsigned long epfn)
>          return 0;
>  
>      /* Make sure the new range is not present now */
> -    sidx = ((pfn_to_pdx(spfn) + PDX_GROUP_COUNT - 1)  &
> ~(PDX_GROUP_COUNT - 1))
> -            / PDX_GROUP_COUNT;
> +    sidx = (pfn_to_pdx(spfn) & ~(PDX_GROUP_COUNT - 1)) /
> PDX_GROUP_COUNT;
>      eidx = (pfn_to_pdx(epfn - 1) & ~(PDX_GROUP_COUNT - 1)) /
> PDX_GROUP_COUNT;
> -    if (sidx >= eidx)
> -        return 0;
> -
>      s = find_next_zero_bit(pdx_group_valid, eidx, sidx);
>      if ( s > eidx )
>          return 0;

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