Re: NMI Injection to Guest

[Gleb Natapov <gleb@redhat.com>]

On Sat, Aug 01, 2009 at 05:36:16PM +0200, Jiaqing Du wrote:
> Hi Gleb,
> 
> Another problem on AMD processors.
> 
> After each vm-exit, I need to check if this vm-exit is due to NMI. For
> vmx.c, I add the check in vmx_complete_interrupts().
> 
> The code snippet is:
> 
> 3539         if ((exit_intr_info & INTR_INFO_INTR_TYPE_MASK) ==
> INTR_TYPE_NMI_INTR &&
> 3540             (exit_intr_info & INTR_INFO_VALID_MASK)) {
> 3541
> 3542                 printk(KERN_INFO "kvm-oprofile: vm exit due to NMI.\n");
> 3543
> 3544                 /* indicate vm-exit due to conter overflow */
> 3545                 vcpu->vm_exit_on_cntr_overflow = 1;
> 3546         }
> 
> This works on Intel chips.
> 
> I did the similar check in svm_complete_interrupts().
> 
> 2501 static void svm_complete_interrupts(struct vcpu_svm *svm)
> 2502 {
> 2503         u8 vector;
> 2504         int type;
> 2505         u32 exitintinfo = svm->vmcb->control.exit_int_info;
> 2506         struct kvm_vcpu *vcpu = &svm->vcpu;
> 2507
> 2508         if (svm->vcpu.arch.hflags & HF_IRET_MASK)
> 2509                 svm->vcpu.arch.hflags &= ~(HF_NMI_MASK | HF_IRET_MASK);
> 2510
> 2511         svm->vcpu.arch.nmi_injected = false;
> 2512         kvm_clear_exception_queue(&svm->vcpu);
> 2513         kvm_clear_interrupt_queue(&svm->vcpu);
> 2514
> 2515         if (!(exitintinfo & SVM_EXITINTINFO_VALID))
> 2516                 return;
> 2517
> 2518         vector = exitintinfo & SVM_EXITINTINFO_VEC_MASK;
> 2519         type = exitintinfo & SVM_EXITINTINFO_TYPE_MASK;
> 2520
> 2521         /* kvm-oprofile */
> 2522         if (type == SVM_EXITINTINFO_TYPE_NMI) {
> 2523
> 2524                 printk(KERN_INFO "kvm-oprofile:
> counter_overflowed & vm exit.\n");
> 2525                 vcpu->vm_exit_on_cntr_overflow = 1;
> 2526         }
> 
> However, this part (2522 to 2526) never got executed. By using qemu
> monitor, I managed to inject NMI to the guests. But this check, after
> vm-exit due to NMI, does not succeed.
> 
> 
The check on AMD is very different from the check on Intel. On AMD you
are checking for IDT access fault during NMI delivery and on Intel you
are checking if the last vmexit was due to NMI delivered to a CPU by HW
while guest was running. On AMD nmi_interception() is called in this
case.

And since MNI interception intercepts only HW NMIs not NMIs that
hypervisor injects your test (using qemu monitor to inject NMI) is
also not valid.

--
			Gleb.