Re: [Xen-devel] supervisor_mode_kernel and hypercall

["pradeep singh rautela" <rautelap@xxxxxxxxx>]

On Mon, Oct 20, 2008 at 3:44 PM, Yanjun Wu <yanjun.wu@xxxxxxxxx> wrote:
>
> In xen/arch/x86/x86_32/traps.c, if supervisor_mode_kernel is true, the
> hypercall_page will be initialized by
> hypercall_page_initialise_ring0_kernel.
> my question is, does supervisor_mode_kernel mean that the guest kernel is
> also running in ring0, the same privilege level as Xen hypervisor?

Yes but in non-root mode. This is possible because some new hardware
extensions added to x86 archtiture by Intel/AMD to facilitate
virtualization.

> The book "the definitive guide to the xen hypervisor" (in page 30) says
> hypercall through int82 is now deprecated, and replaced by hypercall_page.
> but int82 can still be found in hypercall_page_initialise_ring1_kernel. In
> what situation it will be used?

If the new method of hypercall invocation is not supported by the CPU.
I think this should be similar to the way  int 0x80 and
SYSENTER/SYSEXIT are differentiated in linux kernel.

HTH,

Thanks,
    --Pradeep

>
> Thanks.
>
> -Yanjun
>
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>



-- 
Pradeep Singh Rautela
http://eagain.wordpress.com
http://emptydomain.googlepages.com

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