On Fri, Dec 14, 2012 at 04:42:36PM -0700, Alex Williamson wrote:
>
> I don't really know what I'm doing messing around with realmode
> exception handling, but are we missing something like this:
>
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4332,7 +4332,8 @@ static int handle_exception(struct kvm_vcpu *vcpu)
> if (vcpu->arch.halt_request) {
> vcpu->arch.halt_request = 0;
> return kvm_emulate_halt(vcpu);
> - }
> + } else if (vcpu->mmio_needed)
> + return 0;
> return 1;
> }
>
>
> The background is that I was playing around with when the MMIO regions
> of PCI assigned devices get direct mapped through KVM and start using
> memory slots and I found that the boot ROM on an e1000e card that I
> often use for testing causes the VM to hang when not directly mapped
> through a memory slot. This happens with both pci-assign and vfio-pci.
> Debugging further, I see the kernel instruction emulator decodes this
> and sets all the necessary flags and fragments for userspace to complete
> the access, but since it happened in real mode, vcpu_enter_guest always
> returns 1 and therefore KVM_RUN never exits to userspace and KVM gets
> stuck in an infinite loop re-handling this instruction.
>
> The above is pretty trivial and allows the ROM to work again. Is it
> correct? What other exceptions are we missing here that should allow an
> exit? This particular access generated a GP_VECTOR exception if we want
> to key on that somewhere. Thanks,
>
As far as I see the patch is nop. If handle_rmode_exception() returns 1
mmio_needed should be 0. Also if handle_rmode_exception() makes IO
according to the code qemu should exit with "KVM: exception 13 exit
(error code 0x0)" or something. Can you provide a ftrace for the hang?
--
Gleb.
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