Re: Interrupt for HVM guests

[Emre Can Sezer <ecsezer@ncsu.edu>]

Keir Fraser wrote:
> On 05/06/2009 19:43, "Emre Can Sezer" <ecsezer@ncsu.edu> wrote:
>
>   
>> I am trying to figure out how an HVM guest is passed an interrupt.  Say
>> that a network packet has arrived and the QEMU driver in dom0 has to
>> notify an HVM guest of the packet's arrival.  Could someone please give
>> a brief, high-level description of this process?  I read the Intel
>> Architectures Software Developer's Guide on VM Execution bits and
>> Virtual interrupts and also some Xenwiki stuff about it but I'm still
>> not sure what's going on.  I don't have any device pass-through or
>> stubdom or PV Drivers for my HVM guest.  I would also appreciate
>> references to some Xen files/functions related to this process.
>>     
>
> Following will give you enough to grep around for the details:
> Hypercall is HVMOP_set_pci_intx_level: qemu-dm uses this to assert a PCI
> INTx virtual interrupt line. Handled by hvm_pci_intx_assert() ->
> vioapic_irq_positive_edge() -> vioapic_deliver() -> ioapic_inj_irq() ->
> vlapic_set_irq()&vcpu_kick(). Final function there wakes the guest vcpu
> which on vmentry calls vmx_intr_assist() -> hvm_vcpu_has_pending_irq() ->
> vlapic_has_pending_irq(), which will return a pending vector.
> Vmx_intr_assist() then delivers that vector via vmx_inject_extint().
> Hardware then delivers the interrupt automatically during vmentry.
>
>  -- Keir
>
>   
Thanks Keir.  I do have another question though.  I am trying to find 
out whether a page fault occurred during an interrupt handling.  I 
implemented two page tables for HVM guests that help me track execution 
within the guest kernel.  So there is a very good chance that an 
interrupt might also result in a page fault as soon as it is injected.  
I tried counting these events by checking the IF flags in regs->rflags 
and also looking at VIF and VIP flags without success.  Is this a viable 
method for determining whether a page fault was caused during interrupt 
handling?  If not, is there any VM state I can check?

Thanks,

John