Re: [Qemu-devel] [PATCH v4 5/5] kvm/x86: Hyper-V kvm exit

[Pavel Fedin]

 Hello!

 I realize that it's perhaps too late, because patches are already on 
Linux-next, but i have one concern... May be it's not too
late...

 I dislike implementing architecture-dependent exit code where we could 
implement an architecture-independent one.

 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?

 This would allow us to solve the same task which we have done here, but this 
solution would be reusable for other devices and other
archirectures. What if in future we have more system registers to emulate in 
userspace?

 I write this because at one point i suggested similar thing for ARM64 (but i 
never actually wrote it), to emulate physical CP15
timer. And it would require exactly the same capability - process some trapped 
system register accesses in userspace.

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia