Re: [Xen-devel] Updating built-in GDT

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 23 Jan 2006, at 18:02, Ivan Kelly wrote:

> When porting a new OS to xen (using 2.0.7) is it possible to use the 
> builtin
> GDT for all your purposes, or do you have to create a new one if you 
> want to
> work with anything but the descriptors that are already in the xen 
> provided
> one.
> If you can use the builtin one, how do you access the GDT? Is it in 
> the 64M
> reserved address space?
You can't update the built-in GDT. Instead, create your own and pass 
the list of MFNs that comprise your GDT to the set_gdt() hypercall. You 
must ensure you have only read-only mappings of those MFNs before 
passing them to that hypercall! If you wish to update your GDT, use the 
update_descriptor() hypercall.
We could emulate write accesses to the guest GDT, but that hasn't so 
far been implemented.
 -- Keir


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