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xen-devel
Re: [Xen-devel] Xen as a kernel module
> > Right now Xen is mapped somewhere in top of memory, I am not sure how
> > domains are kept out of there, but I suppose it has to do with segments.
>
> As I understand this xen runs in ring0 and pushes the guests kernels one
> ring up into ring1 and then uses traps to allow the guest OSes to trap into
> the hypervisor as necessary.
Yup. Xen is mapped into the top 64MB of virtual address space of every
process (just above the Linux kernel). Segmentation is indeed used to ensure
that:
* user processes can only see their own memory
* guest kernels can see their own memory and user process memory
* Xen can see guest kernel memory and user process memory within the guest
This is a straightforward extension of the way segments are used in vanilla
Linux on x86.
Cheers,
Mark
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