[Xen-devel] [RFC] x86_64 and protection

[Mathieu Ropert <mro@xxxxxxxxxx>]

Hi,

i'm trying to understand how protection with Xen on x86_64 has kernel 
and user code run on the same privilege level.
Things i'm wondering:
- As all kernel pages must mapped with USER bit, how do i make sure user 
process can't access them? Unmap all before switching to user mode?
- How Xen makes the difference between a kernel and a user process? I 
think it use a software flag or something to handle syscall instruction 
properly (ie: processing hypercall or give control to kernel syscalls 
management depending on the caller).
Some documentations on this would be great for future attempts to port 
other OS to Xen.
Regards,

Mathieu

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