[Xen-devel] Re: [PATCH][HVM] fix VNIF restore failure on HVM guest with heavy workload

["Zhai, Edwin" <edwin.zhai@xxxxxxxxx>]

On Tue, Apr 10, 2007 at 08:16:04PM +0100, Keir Fraser wrote:
> On 10/4/07 17:47, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx> wrote:
> 
> > [PATCH][HVM] fix VNIF restore failure on HVM guest with heavy workload
> > 
> > Signed-off-by: Zhai Edwin <edwin.zhai@xxxxxxxxx>
> > 
> > VNIF has many intrs when save/restore with net workload, so need keep 
> > handler
> > from intrs
> 
> What happens if an interrupt is being processed during save/restore? It
> would be nice to know what the underlying bug is!

If an pseudo PCI intr occurred after xen_suspend on cpu0, there is definitely a 
crash. I copy this code from original PV driver code.

> 
> That said, it may well make sense to somehow disable interrupt handling
> across save/restore. Unfortunately your patch is insufficient since we could
> handle event-channel interrupts on any VCPU (the irq's affinity can be
> changed outside our control if it is routed through the virtual IOAPIC, and
> if e.g. the userspace irqbalance daemon is running).
> 
> I wanted to use stop_machine_run() but unfortunately it isn't exported to
> modules. :-( irq_disable() may do the right thing for us though.

SMP is a headache for PV drv save/restore on HVM. Even we disable intr on all 
cpus, PV driver on other cpu may still access low level service after 
xen_suspend on cpu0.

smp_suspend is used for PV drv on PV domain, which is not suitable for HVM as 
we 
need the transparency to guest.

Do we need lightweight stop_machine_run in this case, i.e. make other cpu sleep?


> 
>  -- Keir
> 

-- 
best rgds,
edwin

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