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Re: [Xen-devel] Capturing CPL changes

To: Emre Can Sezer <ecsezer@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Capturing CPL changes
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 03 Sep 2008 20:00:04 +0100
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It is not easy to cause a VMEXIT on execution of SYSCALL. The reads of the
SYSCALL MSRs which the processor must internally execute as part of this
instruction are not interceptable like normal RDMSR instructions.

 -- Keir

On 3/9/08 19:29, "Emre Can Sezer" <ecsezer@xxxxxxxx> wrote:

> Hi, I've set up a 64-bit HVM guest and was wondering if there is anyway I
> can determine when the privilege level escalates to 0.  My goal is to
> determine when execution jumps to the guest kernel.  This includes
> external interrupts as well as internal ones like system calls.
> I've read through the source code especially vmx.c, vmcs.c and exit.S as
> well as the intel documentation on vmx, yet I couldn't figure out if I can
> set  the bitmap so that system calls cause a VMEXIT.
> Is there a way I can capture whenever execution jumps into kernel?  I've
> enabled MSR read/writes to cause VMEXIT's but even then I don't see a read
> from VMX_SYSENTER_CS/EIP/ESP.  I don't know if setting the MSR_GS_BASE or
> MSR_FS_BASE is any indication.
> I'm thinking about setting the debug registers in the VM so that the
> system call entry points trap into the VMM.
> I appreciate any help or advice on the matter.
> Thanks in advance,
> John
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