On 12/21/2015 04:28 PM, Pavel Fedin wrote:
Hello!
Yes, we can use KVM_EXIT_REG_IO/MSR_IO for Hyper-V SynIC MSRS's changes
and can even use only one MSR value . So union inside struct
kvm_hyperv_exit is excessive.
But we still need Vcpu exit to handle VMBus hypercalls by QEMU to
emulate VMBus devices inside QEMU.
And currently we are going to extend struct kvm_hyperv_exit
to store Hyper-V VMBus hypercall parameters.
Hm... Hypercalls, you say?
We already have KVM_EXIT_HYPERCALL. Documentation says it's currently unused. Is it a leftover from ia64 KVM? Could we reuse it for
the purpose?
but could we replace Hyper-V VMBus hypercall and it's parameters
by KVM_EXIT_REG_IO/MSR_IO too?
It depends. Can i read about these hypercalls somewhere? Is there any documentation?
I don't know about a documentation, but you can look at the code of
Hyper-V hypercall handling inside KVM:
https://github.com/torvalds/linux/blob/master/arch/x86/kvm/hyperv.c#L346
The code simply decodes hypercall parameters from vcpu registers then
handle hypercall code in switch and encode return code inside vcpu
registers. Probably encode and decode of hypercall parameters/return
code can be done in QEMU so we need only some exit with parameter that
this is Hyper-V hypercall and probably KVM_EXIT_HYPERCALL is good for it.
But KVM_EXIT_HYPERCALL is not used inside KVM/QEMU so requires
implementation.
Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia
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