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Date: Fri, 27 Sep 2013 12:50:32 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] Capture SIGSEGV to track pc.ram page access
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To: Thomas Knauth <thomas.knauth@gmx.de>
Cc: qemu-devel@nongnu.org

On Thu, Sep 26, 2013 at 02:53:54PM +0200, Thomas Knauth wrote:
> As far as I understand the dirty logging infrastructure will only
> record writes. I want to track reads as well.
> 
> A better way to express what I would like to do is trace all guest
> physical addresses that are accessed. Again, I am unsure whether qemu
> supports this out-of-the box and where I would have to add/modify the
> source to do so.

If you want to continue with the original SIGSEGV handler approach,
check signals masks for the vcpu threads.  Make sure the signal actually
gets delivered to a thread that has the signal unblocked and a signal
handler installed.

Regarding dirty logging, you could try modifying the KVM dirty logging
code to also trap reads.

Also take a look at /proc/PID/pagemap and documentation on accessing
this page table info.  It can be used for tracking dirty pages
("soft-dirty") but I'm not sure if it reports accessed pages.

Stefan