Re: [Xen-devel] supervisor_mode_kernel and hypercall

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 20/10/08 11:14, "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? 
>
> 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? 

Yes, supervisor_mode_kernel means that the dom0 kernel runs in ring 0. It also means that other guests cannot be run. It’s not really very useful these days.

To your other question: guests are supposed to call into the hypervisor via the hypercall page, but actually the underlying mechanism is still int 0x82 for 32-bit PV guests. It’s just hidden in the hypervisor-provided hypercall page now.

 -- Keir



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