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Re: [Xen-devel] [PATCH] Allow wake up of offline vcpu via nmi-ipi

  • To: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir.xen@xxxxxxxxx>
  • Date: Wed, 18 Jan 2012 09:31:28 +0000
  • Delivery-date: Wed, 18 Jan 2012 09:32:19 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AczVw/Q+Cjbk8B14+Uy6l0c+PxeTZw==
  • Thread-topic: [Xen-devel] [PATCH] Allow wake up of offline vcpu via nmi-ipi

On 18/01/2012 09:07, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx> wrote:

> On 01/18/2012 09:48 AM, Juergen Gross wrote:
>> On a real machine a cpu disabled via hlt with interrupts disabled can be
>> reactivated via a nmi ipi. Enable the hypervisor to do this for hvm, too.
>> Signed-off-by: juergen.gross@xxxxxxxxxxxxxx
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>> xen/arch/x86/hvm/vlapic.c |    5 ++++-
> BTW: I was not able to reactivate a vcpu via INIT/SIPI/SIPI sequence. It works
> on initial system boot when the target vcpu is activated the first time. If I
> deactivate a vcpu and try to activate it again it will start to run, but it is
> not starting at the specified entry point (at least it isn't performing the
> first instruction there).
> Is there some special initialization needed to make this work? Do I have to
> reset
> something on the vcpu before deactivating it?

No it should just work. Hvmloader wakes and then sleeps every AP, in
hvmloader/smp.c. So even the first INIT-SIPI wakeup of an AP in the guest OS
is not the first, as hvmloader already did it once! So this path should be
working and indeed tested on every HVM guest boot.

 -- Keir

> Juergen

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