Re: [Xen-devel] [PATCH RFC V2 4/6] xen: Support for VMCALL mem_events

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.03.15 at 15:07, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> Yes, but Andrew's idea (which I think is very neat) is that instead of
> the trickery I used to do in the original patch (create a specific
> VMCALL vm_event and compare eax to a magic constant on VMCALL-based
> VMEXITS, to figure out if all I wanted to do was send out the event),
> that I should instead have the guest set up rax, rdi and rsi and execute
> vmcall, which would then be translated to a real hypercall that sends
> out a vm_event.

If you think about a bare HVM guest OS (i.e. without any PV
drivers), then of course you should provide such hypercall
wrappers for code to use instead of open coding it in potentially
many places.

> In this case, the (HVM) guest does need to concern itself with what
> registers it should set up for that purpose. I suppose a workaround
> could be to write the subop in both ebx and rdi, though without any
> testing I don't know at this point what, if anything, might be broken
> that way.

Guest code ought to know what mode it runs in. And introspection
code (in case this is about injection of such code) ought to also
know which mode the monitored guest is in.

Jan


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