RE: [Xen-devel] credit scheduler issues in 64bit hypervisor

["Li, Xin B" <xin.b.li@xxxxxxxxx>]

>>I am also seeing an instant reboot if I try the credit
>>scheduler on my x86-64 system.  The reboot happens every
>>time I try to start a VT guest domain - haven't tried
>>paravirt, since I need one of the VT domains :)
>
>Have you got any debug output from Xen ? (and are you running a debug 
>build?). 
>
>>Please don't make the credit scheduler the default until
>>it actually works.
>
>I'm not sure this is a credit scheduler bug - it seems rather 
>more likely
>to be a vmx bug shaken out by the more aggressive load 
>balancing of the 
>new scheduler. Masking such bugs by using another scheduler 
>doesn't seem
>like a great idea to me.
>

This is caused by a vmcs bug, the root cause is on x86_64, a VMX domain
is killed without any vmentry (caused by "Error: Device 768 (vbd) could
not be connected. Hotplug scripts not working."), but then a VMCLEAR is
still executed on its unlaunched VMCS.
the following patch fixes it.

Signed-off-by: Xin Li <xin.b.li@xxxxxxxxx>

diff -r 130a5badf2b7 xen/arch/x86/hvm/vmx/vmcs.c
--- a/xen/arch/x86/hvm/vmx/vmcs.c       Fri Jun 30 22:02:58 2006 +0100
+++ b/xen/arch/x86/hvm/vmx/vmcs.c       Sat Jul 01 23:10:31 2006 +0800
@@ -67,7 +67,12 @@ static void __vmx_clear_vmcs(void *info)
 static void __vmx_clear_vmcs(void *info)
 {
     struct vcpu *v = info;
+
+    if ( !v->arch.hvm_vmx.launched )
+        return;
+
     __vmpclear(virt_to_maddr(v->arch.hvm_vmx.vmcs));
+
     v->arch.hvm_vmx.active_cpu = -1;
     v->arch.hvm_vmx.launched   = 0;
 }

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