Messages in this thread | | | Date | Tue, 18 Aug 2009 14:15:57 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver objects |
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On 08/18/2009 02:07 PM, Michael S. Tsirkin wrote: > On Tue, Aug 18, 2009 at 01:45:05PM +0300, Avi Kivity wrote: > >> On 08/18/2009 01:28 PM, Michael S. Tsirkin wrote: >> >>> >>>> Suppose a nested guest has two devices. One a virtual device backed by >>>> its host (our guest), and one a virtual device backed by us (the real >>>> host), and assigned by the guest to the nested guest. If both devices >>>> use hypercalls, there is no way to distinguish between them. >>>> >>>> >>> Not sure I understand. What I had in mind is that devices would have to >>> either use different hypercalls and map hypercall to address during >>> setup, or pass address with each hypercall. We get the hypercall, >>> translate the address as if it was pio access, and know the destination? >>> >>> >> There are no different hypercalls. There's just one hypercall >> instruction, and there's no standard on how it's used. If a nested call >> issues a hypercall instruction, you have no idea if it's calling a >> Hyper-V hypercall or a vbus/virtio kick. >> > userspace will know which it is, because hypercall capability > in the device has been activated, and can tell kernel, using > something similar to iosignalfd. No? >
The host kernel sees a hypercall vmexit. How does it know if it's a nested-guest-to-guest hypercall or a nested-guest-to-host hypercall? The two are equally valid at the same time.
>> You could have a protocol where you register the hypercall instruction's >> address with its recipient, but it quickly becomes a tangled mess. >> > I really thought we could pass the io address in register as an input > parameter. Is there a way to do this in a secure manner? > > Hmm. Doesn't kvm use hypercalls now? How does this work with nesting? > For example, in this code in arch/x86/kvm/x86.c: > > switch (nr) { > case KVM_HC_VAPIC_POLL_IRQ: > ret = 0; > break; > case KVM_HC_MMU_OP: > r = kvm_pv_mmu_op(vcpu, a0, hc_gpa(vcpu, a1, a2),&ret); > break; > default: > ret = -KVM_ENOSYS; > break; > } > > how do we know that it's the guest and not the nested guest performing > the hypercall? >
The host knows whether the guest or nested guest are running. If the guest is running, it's a guest-to-host hypercall. If the nested guest is running, it's a nested-guest-to-guest hypercall. We don't have nested-guest-to-host hypercalls (and couldn't unless we get agreement on a protocol from all hypervisor vendors).
-- error compiling committee.c: too many arguments to function
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