Re: [RFC][PATCH 1/2] kvm: x86: mmu: return zero if s > e in rsvd_bits()

[Paolo Bonzini <pbonzini@redhat.com>]

On 14/11/2014 10:31, Tiejun Chen wrote:
> In some real scenarios 'start' may not be less than 'end' like
> maxphyaddr = 52.
> 
> Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
> ---
>  arch/x86/kvm/mmu.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index bde8ee7..0e98b5e 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -58,6 +58,8 @@
>  
>  static inline u64 rsvd_bits(int s, int e)
>  {
> +	if (unlikely(s > e))
> +		return 0;
>  	return ((1ULL << (e - s + 1)) - 1) << s;
>  }
>  
> 

s == e + 1 is supported:

   (1ULL << (e - (e + 1) + 1)) - 1) << s ==
   (1ULL << 0) << s ==
   0

Is there any case where s is even bigger?

Paolo