[Xen-devel] Question to xenoprof and user/kernel mode

To:	xen-devel@xxxxxxxxxxxxxxxxxxx
Subject:	[Xen-devel] Question to xenoprof and user/kernel mode
From:	Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxxxxxxx>
Date:	Tue, 29 Apr 2008 16:37:55 +0200
Cc:	joserenato.santos@xxxxxx
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Hi list,

I looked at the xenoprof, did some sampling and got results I don't fully 
understand.
First I tried to sample dom0 user events with
--event CPU_CLK_UNHALTED:100000:0:0:1
Here I saw samples from dom0 user and dom0 kernel. This is OK for me because 
dom0 kernel runs with cpl 3 too. But there were some samples from the 
hypervisor too (symbol validate_gl3e).

Then I tried to sample only do0 kernel events with
--event CPU_CLK_UNHALTED:100000:0:1:0
what means sampling only in cpl 0. But I got samples from dom0-kernel, 
hypervisor and few samples from the user land in dom0 too.

The conclusion is that it seems that sometimes user runs in cpl 0 and 
sometimes hypervisor in cpl > 0.
As I understand from the spec a vmexit leads always to cpl 0. So hypervisor 
code should never run in cpl > 0?
But is there a possibility where user land code runs in cpl 0 in few cases?

Please can anybody give me a light on this behavior or a link in doc or 
source!
Thanks.

Dietmar.

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