[Xen-changelog] [xen-unstable] SVM: fix performance decrease with asid assignment

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Christoph Egger <Christoph.Egger@xxxxxxx>
# Date 1339581086 -7200
# Node ID 34c725807d21451f50e7dc4ece36b137b8b35169
# Parent  bc2f3a848f9a7c23b4a3736d0215732b1f039219
SVM: fix performance decrease with asid assignment

Do not clear asid cleanbit unconditionally. This shaves off 100 cycles
from the VMRUN instruction.

Signed-off-by: Christoph Egger <Christoph.Egger@xxxxxxx>
Committed-by: Jan Beulich <jbeulich@xxxxxxxx>
---


diff -r bc2f3a848f9a -r 34c725807d21 xen/arch/x86/hvm/svm/asid.c
--- a/xen/arch/x86/hvm/svm/asid.c       Tue Jun 12 11:33:42 2012 +0100
+++ b/xen/arch/x86/hvm/svm/asid.c       Wed Jun 13 11:51:26 2012 +0200
@@ -56,7 +56,8 @@ void svm_asid_handle_vmrun(void)
         return;
     }
 
-    vmcb_set_guest_asid(vmcb, p_asid->asid);
+    if (vmcb_get_guest_asid(vmcb) != p_asid->asid)
+        vmcb_set_guest_asid(vmcb, p_asid->asid);
     vmcb->tlb_control = need_flush;
 }
 

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