Xen devel - Feb 2004 - Re: [Xen-announce] Questions about the control tools in Xen

> Recently, I have traced part of the Xen VMM code.
> 
> but I have some troubles...
> 
> I could not find out the function ioctl() which is called by the function
do_privcmd() (xeno-1.2.bk/tools/xc/lib/xc_private.h)
"man ioctl" -- its a system call
> Is the interface between guest OS and VMM just like the interface between
OS and Hardware ?
Similar, but different. The best overview description is in the
SOSP paper available off the project web page.
> Is there any protection in Xen VMM to protect that only Domain 0 could use
the control tools?
Yes. There''s a concept of a ''privileged domain'' that
all dom0_ops
and other hypervisor interfaces check. In future, we may allow
delegations to enable, for example, domain 3 to be able to
control and manipulate domain 7 but no others.

Best,
Ian


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----- Original Message ----- 
From: "Ian Pratt" <Ian.Pratt@cl.cam.ac.uk>
To: "Inaba" <B8844014@stmail.cgu.edu.tw>
Cc: "Xen VMM Maillist" <xen-devel@lists.sourceforge.net>;
<Ian.Pratt@cl.cam.ac.uk>
Sent: Thursday, February 12, 2004 4:23 PM
Subject: Re: [Xen-announce] Questions about the control tools in Xen

>
> > Recently, I have traced part of the Xen VMM code.
> >
> > but I have some troubles...
> >
> > I could not find out the function ioctl() which is called by the
function do_privcmd()
(xeno-1.2.bk/tools/xc/lib/xc_private.h)
>
> "man ioctl" -- its a system call
I got it , thanks a lot !!!
>
> > Is the interface between guest OS and VMM just like the interface
between OS and Hardware ?
>
> Similar, but different. The best overview description is in the
> SOSP paper available off the project web page.
I''m reading this paper now, but I could not understand how guest OS set
into
kernel mode from ring 3 into ring 1 insteed of ring 3 into ring 0.

which functions or codes need to be modified in Xenolinux source code?
>
> > Is there any protection in Xen VMM to protect that only Domain 0 could
use the control tools?
>
> Yes. There''s a concept of a ''privileged domain''
that all dom0_ops
> and other hypervisor interfaces check. In future, we may allow
> delegations to enable, for example, domain 3 to be able to
> control and manipulate domain 7 but no others.
I''m not really understand the concept ''privileged
domain''  means.

but I have traced some of codes in xen.

I found that pyxc_domain_create() would call the function
xc_domain_create() -> do_dom0_op() -> do_xen_hypercall() ->
do_privcmd() ->
ioctl()

In xc_domain_create() would fill in some parameters into dom0_op_t data
structure.

But if another domain such as domain 1 calls the function
pyxc_domain_create(), then it would create another domain ??

I guess that in Xen VMM it would check the the request of operations comes
from which domain. (domain number or address space ???)

If I want to know the protection mechanism which function I need to trace ?

Cheers,

Inaba
>
> Best,
> Ian
>




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