Re: vcpu_info

[Jeremy Fitzhardinge <jeremy@goop.org>]

pallavi jk wrote:
> Hi Jeremy,
>
> Yes, I am planning to modify xen and the guest OS as well.
>
> I need to trap every entry into the guest OS from user mode because I 
> need to perform some checks in the hypervisor before transferring 
> control to the guest OS.

If you run a 64-bit hypervisor, this will happen automatically.  Only 
32-on-32 supports directly trapping from guest usermode to kernel.

> So I need to avoid fast handlers which would directly transfer control 
> to the guest OS, as I want to trap this entry first in the hypervisor. 
> I need to do this as I intend to protect applications from a possibly 
> malicious OS, so I want to perform some checks in the hypervisor.
>
> I have just started studying the code. Can you please provide me 
> guidelines about which source files and functions I should concentrate 
> on?

arch/x86/**/traps.c is the first point to look at. Also entry.S which 
does the actual transfer of control between the various modes.  There 
are several variants of each file for different modes (32, 64, 32 compat 
on 64), so make sure you target the right ones.

    J