[Xen-devel] [VMI] How to add support for MOV-TO-DRx events ?

[Mathieu Tarral <mathieu.tarral@xxxxxxxxxxxxxx>]

Hi,

following a previous conversation, i would like to catch MOV-TO-DRx VMI events 
to prevent the guest from disabling my hardware breakpoints.

@Tamas pointed me to this header:
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/include/public/vm_event.h;h=b2bafc0d77f9758e42b0d53c05a7e6bb86c86686;hb=HEAD#l154

And, as far as I can tell, I have to
- add a new REASON
#define VM_EVENT_REASON_WRITE_DEBUGREG      15

- add a new struct
struct vm_event_write_debugreg {
    uint32_t index;
    uint32_t _pad;
    uint64_t new_value;
    uint64_t old_value;
};

- insert it into the vm_event_st union

Can you give me more pointer and guidance how to implement this into Xen ?
I have never submitted a patch, nor looked into Xen source code.

Should we create a single event for MOV-TO-REGx VMI events ?
It would void copy pasting and duplicating code.

Thanks !


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