Re: [PATCH] KVM: VMX: Translate interrupt shadow when waiting on NMI window

[Gleb Natapov <gleb@redhat.com>]

On Tue, Feb 16, 2010 at 10:16:12AM +0100, Jan Kiszka wrote:
> Found while browsing Xen code: While we assume that the STI interrupt
> shadow also inplies virtual NMI blocking, some processors may have a
> different opinion (SDM 3: 22.3). To avoid misunderstandings that would
> cause endless VM entry attempts, translate STI into MOV SS blocking when
> requesting the NMI window.
> 
Why not just remove "block by STI" check in vmx_nmi_allowed()? IIRC this
is documented that on some CPUs STI does not block NMI.

> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
>  arch/x86/kvm/vmx.c |   15 +++++++++++++++
>  1 files changed, 15 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 14873b9..474f720 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2614,12 +2614,27 @@ static void enable_irq_window(struct kvm_vcpu *vcpu)
>  static void enable_nmi_window(struct kvm_vcpu *vcpu)
>  {
>  	u32 cpu_based_vm_exec_control;
> +	u32 interruptibility;
>  
>  	if (!cpu_has_virtual_nmis()) {
>  		enable_irq_window(vcpu);
>  		return;
>  	}
>  
> +	/*
> +	 * SDM 3: 22.3 (June 2009)
> +	 * "A logical processor may also prevent such a VM exit [NMI-window
> +	 * exit] if there is blocking of events by STI."
> +	 * So better convert STI blocking into MOV SS to avoid premature VM
> +	 * exits that would end up in an endless loop.
> +	 */
> +	interruptibility = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
> +	if (interruptibility & GUEST_INTR_STATE_STI) {
> +		interruptibility &= ~GUEST_INTR_STATE_STI;
> +		interruptibility |= GUEST_INTR_STATE_MOV_SS;
> +		vmcs_write32(GUEST_INTERRUPTIBILITY_INFO, interruptibility);
> +	}
> +
>  	cpu_based_vm_exec_control = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
>  	cpu_based_vm_exec_control |= CPU_BASED_VIRTUAL_NMI_PENDING;
>  	vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control);

--
			Gleb.