[PATCH 1/1] arch/x86/kvm/vmx.c: Fix external interrupts inject directly bug with guestos RFLAGS.IF=0

[Li Kaihang]

This patch fix a external interrupt injecting bug in linux 3.19-rc4.

GuestOS is running and handling some interrupt with RFLAGS.IF = 0 while a external interrupt coming,
then can lead to a vm exit,in this case,we must avoid inject this external interrupt or it will generate
a processor hardware exception causing virtual machine crash.

Now, I show more details about this problem:

A general external interrupt processing for a running virtual machine is shown in the following:

Step 1:
     a ext intr gen a vm_exit --> vmx_complete_interrupts --> __vmx_complete_interrupts --> case INTR_TYPE_EXT_INR: kvm_queue_interrupt(vcpu, vector, type == INTR_TYPE_SOFT_INTR);

Step 2:
     kvm_x86_ops->handle_external_intr(vcpu);

Step 3:
     get back to vcpu_enter_guest after a while cycle,then run inject_pending_event

Step 4:
     if (vcpu->arch.interrupt.pending) {
		kvm_x86_ops->set_irq(vcpu);
		return 0;
	}

Step 5:
     kvm_x86_ops->run(vcpu) --> vm_entry inject vector to guestos IDT

for the above steps, step 4 and 5 will be a processor hardware exception if step1 happen while guestos RFLAGS.IF = 0, that is to say, guestos interrupt is disabled.
So we should add a logic to judge in step 1 whether a external interrupt need to be pended then inject directly, in the process, we don't need to worry about
this external interrupt lost because the next Step 2 will handle and choose a best chance to inject it by virtual interrupt controller.


Signed-off-by: Li kaihang <li.kaihang@xxxxxxxxxx>
---
 arch/x86/kvm/vmx.c |   20 ++++++++++++++++++--
 1 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index d4c58d8..e8311ee 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7711,10 +7711,26 @@ static void __vmx_complete_interrupts(struct kvm_vcpu *vcpu,
                break;
        case INTR_TYPE_SOFT_INTR:
                vcpu->arch.event_exit_inst_len = vmcs_read32(instr_len_field);
-               /* fall through */
-       case INTR_TYPE_EXT_INTR:
+               /*
+               * As software and external interrupts may all get here,
+               * we should separate soft intr from ext intr code,and this
+               * will ensure that software interrupts handling process is not
+               * affected by solving external interrupt invalid injecting.
+               */
                kvm_queue_interrupt(vcpu, vector, type == INTR_TYPE_SOFT_INTR);
                break;
+       case INTR_TYPE_EXT_INTR:
+               /*
+               * GuestOS is running and handling some interrupt with
+               * RFLAGS.IF = 0 while a external interrupt coming,
+               * then can lead a vm exit getting here,in this case,
+               * we must avoid inject this external interrupt or it will
+               * generate a processor hardware exception causing vm crash.
+               */
+               if (kvm_x86_ops->interrupt_allowed(vcpu))
+                       kvm_queue_interrupt(vcpu, vector,
+                                       type == INTR_TYPE_SOFT_INTR);
+               break;
        default:
                break;
        }
--

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