Re: [Xen-devel] Mem_event API and MEM_EVENT_REASON_SINGLESTEP

[AP <apxeng@xxxxxxxxx>]

On Fri, Nov 30, 2012 at 12:09 PM, Razvan Cojocaru <rzvncj@xxxxxxxxx> wrote:
>> After you set single stepping on for a VCPU and resume, you should see
>> a single step mem_event soon after. What is the behavior that you are
>> observing? Are you trying this on an UP or SMP guest?
>
> I do see single step mem_events after. I've tried it on a SMP HVM
> Slackware guest. What behaviour am I observing? The gla and gfn values
> are being printed out - but I don't know how to detect a write operation
> based on them. Tim Deegan has kindly suggested that I pass those values

You will not be able to detect a write event based on them as you have
marked the page rwx. One option is to mark the page rx and continue
single stepping the page. The on the next write to that page should
give you a write violation and there you can stop single stepping the
page.

> to a debugger API that I assume Xen has, but I don't think there have
> been any replies on that topic since.
>
> Unfortunately I don't have access to the computer I've written the test
> code on, and it's a rather complicated setup that I can't easily
> duplicate at home, so if you need specific details (gfn/gla values,
> etc.) I'm afraid I'll only be able to provide them on Monday.
>
> Thanks,
> Razvan Cojocaru

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