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xen-devel
RE: [Xen-devel] HVM hypercalls, hvm_hypercall_table
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> George Surka
> Sent: 15 March 2007 19:31
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] HVM hypercalls, hvm_hypercall_table
>
> Hi everyone,
>
> I am running XenEnterprise 3.1.0 (Xen v.3.0.3.0) on x86-32
> hardware. I have noticed that the hvm_hypercall_table is
> initialized for only 6 hypercalls (memory_op, multicall,
> xen_version, event_channel_op, sched_op, and hvm_op). The
> hypercall_page for HVM domain is initialized with HVM exit
> (VMCALL instr.) - all stubs.
The purpose of the hvm_hypercall_table is to support para-virtual
drivers.
You should (generally speaking) not be making other hypercalls from a
fully-virtualized (HVM) domain, as those are potentially not safe. Is
ther a particular hypercall you're after, or is this a generic question
as to why this is?
>
> So, how do I do the other hypercalls (beyond those 6) from
> HVM domain? Do I just have to use INT 0x82 trap without using
> the hypercall-page (without using the HYPERVISOR_* hypercall
> macros in hypercall.h)?
No, you can't make any other hypercalls from fully virtualized domains.
If you need further hypercalls, it may be possible to add further
hypercalls, but I don't believe that a "wholesale" implementation of all
hypercalls available to para-virtual Xen will make sense (and in some
cases would be potentials for crashing the guest and/or hypervisor), so
selective implementation is the key here.
[Many of the hypercalls are implemented to overcome the same problems
that the hardware solves in fully virtualized domains, so duplicating
the solution doesn't actually help anything - just adds more code!]
--
Mats
>
> Why there is just those six hypercalls implemented as HVM-hypercalls?
>
> Thanks.
>
> George
>
>
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