VM_EVENT_FLAG_SET_REGISTERS and sync_vcpu_execstate()

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

Hello,

We've been mostly setting registers by using xc_vcpu_setcontext():

https://github.com/razvan-cojocaru/libbdvmi/blob/master/src/bdvmixendriver.cpp#L504

but lately trying to push as much of that as possible to the
VM_EVENT_FLAG_SET_REGISTERS-related code (i.e. via the vm_event replies)
to save processing time.

So with the xc_vcpu_setcontext() call removed, I've found that there are
cases where vm_event_set_registers() won't work properly unless I kept
the xc_vcpu_getcontext() call. This would appear to be not because of
anything that arch_get_info_guest() does (please see the implementation
for XEN_DOMCTL_getvcpucontext), but because of the vcpu_pause() call, or
more specifically, because of its calling sync_vcpu_execstate().

So it would appear that a sync_vcpu_execstate(v) call is necessary at
the start of vm_event_set_registers() for the vcpu struct instance to be
synchronized with the current VCPU state.

Any objections to a patch with this simple modification?


Thanks,
Razvan

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