Re: [RFC PATCH 16/18] KVM: add kvm_arch_vcpu_prevent_run to prevent VM ENTER when NMI is received

Avi Kivity
2012-06-28T16:48:59Z

On 06/28/2012 09:08 AM, Tomoki Sekiyama wrote:
> Since NMI can not be disabled around VM enter, there is a race between
> receiving NMI to kick a guest and entering the guests on slave CPUs.If the
> NMI is received just before entering VM, after the NMI handler is invoked,
> it continues entering the guest and the effect of the NMI will be lost.
>
> This patch adds kvm_arch_vcpu_prevent_run(), which causes VM exit right
> after VM enter. The NMI handler uses this to ensure the execution of the
> guest is cancelled after NMI.
>
>
> +/*
> + * Make VMRESUME fail using preemption timer with timer value = 0.
> + * On processors that doesn't support preemption timer, VMRESUME will fail
> + * by internal error.
> + */
> +static void vmx_prevent_run(struct kvm_vcpu *vcpu, int prevent)
> +{
> + if (prevent)
> + vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL,
> + PIN_BASED_PREEMPTION_TIMER);
> + else
> + vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL,
> + PIN_BASED_PREEMPTION_TIMER);
> +}

This may interrupt another RMW sequence, which will then overwrite the
control. So it needs to be called only if inside the entry sequence
(otherwise can just set a KVM_REQ_IMMEDIATE_EXIT in vcpu->requests).

--
error compiling committee.c: too many arguments to function