Re: [PATCH v3 1/3] KVM: fix rcu usage warning in kvm_arch_vcpu_ioctl_set_sregs()

From: Avi Kivity
Date: Thu Jan 27 2011 - 08:16:07 EST

On 01/20/2011 05:27 PM, Marcelo Tosatti wrote:
> Before patch:
> real 5m6.493s
> user 3m57.847s
> sys 9m7.115s
> real 5m1.750s
> user 4m0.109s
> sys 9m10.192s
> After patch:
> real 5m0.140s
> user 3m57.956s
> sys 8m58.339s
> real 4m56.314s
> user 4m0.303s
> sys 8m55.774s

Nice. One disadvantageous side effect for the kvm_vcpu_kick path
is that it can race with make_all_cpus_request, which is possibly
doing unrelated, slower work (IPI'ing other vcpus, waiting for

I think we're fine here. The kvm_vcpu_kick() check is

me = get_cpu();
if (cpu != me&& (unsigned)cpu< nr_cpu_ids&& cpu_online(cpu))
- if (atomic_xchg(&vcpu->guest_mode, 0))
+ if (kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE)

even if it did race, ->mode becomes EXITING_GUEST_MODE and we still avoid the IPI. Note that make_all_cpus_request() cleverly checks for != OUTSIDE_GUEST_MODE, so if it loses the race with kvm_vcpu_kick(), it still sends the IPI to be sure the vcpu loop sees vcpu->requests in time.

Looks ok, but lets wait for more careful reviews before applying.

Patches applied.

error compiling committee.c: too many arguments to function

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