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@xxxxxxxxxxx>
> ---
>
> 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.
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