Re: [Xen-devel] 4.2.0-rc4 bug: memory events for CR3 register are broken (working in 4.1.3)

[Navin Patel <navinjpatel336@xxxxxxxxx>]

On Sun, Sep 16, 2012 at 12:35 PM, Keir Fraser <keir.xen@xxxxxxxxx> wrote:

This issue is known and a fix has been proposed. It’s too late for 4.2.0 unfortunately, but will be fixed for 4.2.1.

 -- Keir

On 16/09/2012 16:52, "Navin Patel" <navinjpatel336@xxxxxxxxx> wrote:

Greetings,

I have tested some of my research code watching for CR3 memory events on Xen 4.2.0-rc4, and I have discovered that CR3 events are not being delivered.  This did work properly in 4.1.3, so I think 4.2.0-rc4 may has a bug.

 This feature has been removed maybe?

Crude test  to confirm this can be had by changing tools/tests/xen-access/xen-access.c : replace HVM_PARAM_MEMORY_EVENT_INT3 with HVM_PARAM_MEMORY_EVENT_CR3 and rebuild (line 569 and 571 in 4.2.0-rc4).

Then (while domU is scheduling programs/launching new processes) run like int3 were still the constant value: ./xen-access $DOMID int3

4.1.3: In the switch/case, printf will show "UNKNOWN REASON CODE $C", with c == 3 == MEM_EVENT_REASON_CR3 (no case built to detect CR3 evnets).

4.2.0-rc4: In the switch/case, printf will never show "UNKNOWN REASON CODE 3"

Cheers,
Navin

---

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Keir and Steven, 

Thank you for your work. The proposed patch solved the bug! 

After 4.2.0 is officially released this week, I very much hope that this patch is backported to the 4.2.0 tree. Several distributions like Debian are already building upon 4.2.0 and will not wait for 4.2.1, and without the patch being backported, researchers like me will not be able to use the supported Xen from package repository.  We can compile from source, but if we have a supported version it is better for everyone. (And it is such a simple patch! )

Is this something I can request in formal manner?

Cheers,
Navin

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