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

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On 2014/11/17 17:22, Paolo Bonzini wrote:


On 17/11/2014 02:34, Chen, Tiejun wrote:
On 2014/11/14 18:06, Paolo Bonzini wrote:


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@xxxxxxxxx>
---
   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 << (e - (e + 1) + 1)) - 1) << s
     = (1ULL << (e - e - 1) + 1)) - 1) << s
     = (1ULL << (-1) + 1)) - 1) << s

no,

You're right since I'm seeing "()" wrongly.

Sorry to bother you.

Thanks
Tiejun
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