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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 2 Jul 2006, at 05:01, Li, Xin B wrote:

> > > This patch is itself buggy: Just because a VMCS hasn't been launched
> > > doesn't mean it hasn't been activated on some CPU.
> Hmm, thinking about a VMCS is migrating from cpu A to cpu B, and on 
> cpu A vmclear has been executed, but just before the VMCS is launched 
> on cpu B, the domain is killed, what will happen?
> I'm not sure if vmclear on a VMCS in cleared state is allowed. If not, 
> we still need this fix.
active_cpu will be B in this case, so we'll execute VMCLEAR on CPU B. 
'Launched' is just an extra sub-state of an active VMCS. This is all 
taken from Section 20.1 of Vol. 3 of the Intel Reference Manual.
> > > I think the original
> > > bug would be better fixed by only calling vmx_clear_vmcs() in
> > > vmx_destroy_vmcs() if arch_vmx->vmcs != NULL. Even better
> > would be not
> > > to allocate the VMCS so darn late.
> > Yes, it's buggy, and prevent the first vmclear to a vmcs.
> I found even without my fix the first vmclear to a newly allocated 
> vmcs is prevented, this is because arch_vmx->active_cpu = -1is 
> executed  before vmx_clear_vmcs(v) in construct_vmcs().
> We may workaound it by setting active_cpu to smp_processor_id(), and 
> launched to 1here, but surely this is not what we want.
Yes, that's broken. I'll fix to use __vmx_clear_vmcs().

 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel