RE: [Xen-devel] Why using hypercall_page ?

[Wu Bingzheng <wubingzheng@xxxxxxxxx>]

To invoke hypercall:

1. Not using hypercall_page:

    mov $__HYPERCALL_sched_op, %eax
    int $0x82


2. Using hypercall_page:

    call hypercall_page + __HYPERCALL_sched_op * 32

Besides, using the hypercall_page, guest has to keep a page for hypercall_page.

I do not think the hypercall_page makes the thing much easier.

Is "release guest from hardcoding" the only advantage of using hypercall_page?

Thanks,
Wu

å 2008-10-23åç 09:24 +0800ïTian, Kevinåéï
> >From: Wu Bingzheng
> >Sent: Thursday, October 23, 2008 9:18 AM
> >
> >Hello,
> >
> >I am studing Xen hypercall now. I found that hypercall is invoked via
> >hypercall_page, which is only filled with (in
> >no-hypervisor-kernel-mode ):
> >
> >mov $i, %eax
> >int $0x82
> >ret
> >
> >Why not invoked the hypercall directly by "int $0x82" ? What's the
> >advantage of using hypercall_page?
> >
> 
> This allows guest migrated to a newer/older xen with a different
> hypercall invocation convention. Xen fills hypercall page by its
> convention, and thus release guest from hardcoding specific flow.
> 
> Thanks
> Kevin


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