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    Subject[PATCH 2/2] KVM: make guest mode entry to be rcu quiescent state
    Date
    KVM does not hold any references to rcu protected data when it switches
    CPU into a guest mode. In fact switching to a guest mode is very similar
    to exiting to userspase from rcu point of view. In addition CPU may stay
    in a guest mode for quite a long time (up to one time slice). Lets treat
    guest mode as quiescent state, just like we do with user-mode execution.

    Signed-off-by: Gleb Natapov <gleb@redhat.com>
    ---
    include/linux/kvm_host.h | 9 +++++++++
    1 files changed, 9 insertions(+), 0 deletions(-)

    diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    index 0bc3d37..244413f 100644
    --- a/include/linux/kvm_host.h
    +++ b/include/linux/kvm_host.h
    @@ -591,8 +591,17 @@ static inline int kvm_deassign_device(struct kvm *kvm,

    static inline void kvm_guest_enter(void)
    {
    + BUG_ON(preemptible());
    account_system_vtime(current);
    current->flags |= PF_VCPU;
    + /* KVM does not hold any references to rcu protected data when it
    + * switches CPU into a guest mode. In fact switching to a guest mode
    + * is very similar to exiting to userspase from rcu point of view. In
    + * addition CPU may stay in a guest mode for quite a long time (up to
    + * one time slice). Lets treat guest mode as quiescent state, just like
    + * we do with user-mode execution.
    + */
    + rcu_virt_note_context_switch(smp_processor_id());
    }

    static inline void kvm_guest_exit(void)
    --
    1.7.4.4


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