Re: Threaded IPIs?

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Gregory Haskins wrote:
> Hi guys,
>   While working with the -rt kernel, I have noticed a problem in KVM.
> Specifically, when you stop a VM you sometimes get a "sleep while
> atomic" oopses.  It turns out that the issue is related to an
> smp_function_call IPI that KVM does to remotely flush the VMX hardware
> on shutdown.  The code tries to acquire the global kvm_lock (which is a
> normal spinlock_t, of course converted to rt_mutex on -rt) from the
> interrupt context of the IPI handler.  You know the rest of the
> story....
>
> The obvious solution is to convert the kvm_lock to a raw_spinlock_t.
> However, I really don't want to do this unless we absolutely have to
> since it will just increase latencies for a good portion of the rest of
> KVM.
>   

Are you talking about decache_vcpus_from_cpu() that is called from
hardware_disable()?  Would having the caller acquire the lock solve the
problem?  Then it would be acquired from outside the IPI.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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