On 12/18/2015 09:39 PM, Roman Kagan wrote:
On Fri, Dec 18, 2015 at 10:10:11AM -0800, Peter Hornyack wrote:
On Fri, Dec 18, 2015 at 8:01 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
On 18/12/2015 16:19, Pavel Fedin wrote:
As far as i understand this code, KVM_EXIT_HYPERV is called when one
of three MSRs are accessed. But, shouldn't we have implemented
instead something more generic, like KVM_EXIT_REG_IO, which would
work similar to KVM_EXIT_PIO or KVM_EXIT_MMIO, but carry register
code and value?
Yes, we considered that. There were actually patches for this as well.
However, in this case the register is still emulated in the kernel, and
userspace just gets informed of the new value.
On brief inspection of Andrey's patch (I have not been following
closely) it looks like the kvm_hyperv_exit struct that's returned to
userspace contains more data (control, evt_page, and msg_page fields)
than simply the value of the MSR, so would the desired SynIC exit fit
into a general-purpose exit for MSR emulation?
Frankly I'm struggling trying to recall why we implemented it this way.
Actually all three fields are the values of respective MSRs and I don't
see any necessity to pass all three at the same time when any of them
gets updated. The patch for QEMU adds an exit handler which processes
the fields individually, so I have a strong suspicion that union was
meant here rather than struct.
I hope Andrey will help to shed some light on that when he's back in the
office on Monday; meanwhile I think this peculiarity can be ignored.
Hello!
We have implemented Hyper-V related Vcpu exit not only for Hyper-V SynIC
MSR's changes but also to provide future interface to transfer guest
VMBus hypercalls parameters into QEMU.
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.
SynIC MSR's changes could be replaced by KVM_EXIT_REG_IO/MSR_IO
but could we replace Hyper-V VMBus hypercall and it's parameters
by KVM_EXIT_REG_IO/MSR_IO too?
Roman.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
