Re: [Xen-devel] Mem_event API and MEM_EVENT_REASON_SINGLESTEP

[Razvan Cojocaru <rzvncj@xxxxxxxxx>]

> 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


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