Re: Mem_event API and MEM_EVENT_REASON_SINGLESTEP

[Razvan Cojocaru <rzvncj@gmail.com>]

> 1. I haven't been able to find an example of how single-stepping via the
> mem_event API might work. Can you point me to some code that does this
> (or a paper, etc.)?

This is what I got so far (assume the xen-access.c source code file):

int main(int argc, char *argv[])
{
[...]
     rc = xc_hvm_set_mem_access(xch, domain_id,
                                default_access, ~0ull, 0);
     rc = xc_hvm_set_mem_access(xch, domain_id,
                                default_access, 0,
                                xenaccess->domain_info->max_pages);
     xc_set_hvm_param(xch, domain_id,
                      HVM_PARAM_MEMORY_EVENT_SINGLE_STEP,
                      HVMPME_mode_sync);
[...]
             case MEM_EVENT_REASON_SINGLESTEP:
                 printf("SINGLESTEP: gla: %lx gfn %lx\n",
                        req.gla, req.gfn);
                 // If something to do with gfn/gfa,
                 // stop single-stepping this domain and
                 // start faulting again on page writes.
                 break;

             case MEM_EVENT_REASON_VIOLATION:
                 [...]
                 if ( default_access != after_first_access ) {
                     rc = xc_hvm_set_mem_access(xch, domain_id,
                                                after_first_access,
                                                req.gfn, 1);
                     xc_domain_debug_control(xch, domain_id,
                          XEN_DOMCTL_DEBUG_OP_SINGLE_STEP_ON,
                          req.vcpu_id);
                 }
[...]
}

Not quite sure what to do with gla and gfn except print them out at this 
point, though. Again, the condition for stopping single-step mode is 
that a page write happened. Any help is appreciated.

Thanks,
Razvan Cojocaru