On 15/01/2015 13:36, Li Kaihang wrote:
> 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.
I do not understand what is happening here.
Between the time the processor starts delivering an external interrupt
to the VM, and the time it decides to do a vm exit because of an
external interrupt in the host, IF becomes 0.
What is the cause of the external interrupt? Why does IF become 0?
> 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
How did the external interrupt cause the IDT-vectoring information field
to be set? External interrupts for the host are not among the causes
listed in "27.2.3 Information for VM Exits During Event Delivery".
> --> 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);
Why is this relevant? The external interrupt is a vectored event, so it
sets VM-exit interruption information (27.2.2 Information for VM Exits
Due to Vectored Events). It doesn't set the IDT-vectoring information
field.
Paolo
> 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.
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