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

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 01/18/2012 10:36 AM, Keir Fraser wrote:
> On 18/01/2012 09:31, "Keir Fraser"<keir.xen@xxxxxxxxx>  wrote:
>
> > 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.
> Bit more info: INIT-SIPI logic is complicated by needing to avoid deadlocks
> between two VCPUs attempting to pause and reset each other. But the core
> dispatch logic is in vlapic_init_sipi_action(). You will see that on INIT,
> we should call vcpu_reset() which will de-initialise and VCPU_down the vcpu.
> And then on SIPI we call hvm_vcpu_reset_state(), which should reinitialise
> and wake the vcpu to start running at the specified CS:IP.
>
> So the above will be good places for you to add tracing and work out what's
> going on. :-)
Yeah, thanks for the confirmation this should work.
Printing some diagnostics helped me to spot the error in my code.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
PDG ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
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