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Re: [Xen-devel] [PATCH for-4.5 v6 08/16] xen: Add limited support of VMware's hyper-call rpc

On 09/22/14 09:47, Ian Campbell wrote:
On Sat, 2014-09-20 at 14:07 -0400, Don Slutz wrote:
This interface is an extension of __HYPERVISOR_HVM_op.  It was
picked because xc_get_hvm_param() also uses it and VMware guest
info is a lot like a hvm param.
Sorry if this has been discussed before, but did you consider doing all
this in qemu rather than Xen?

Yes, but QEMU does not have access to the VCPU registers. Also QEMU does not have this code; so would also need it to be added.

A second part would be adding a way for a tool stack to
communicate with QEMU to access this data.  xenstore/xenbus might
be one way to do this.

Unless there are frequent accesses to these things then qemu would be
the default best place for this sort of thing, especially since as
you've observed there is some pretty complex memory management and
string handling which it would generally be better to avoid in the

The more complex memory management is around not using the
heap during a single guest instruction (inl (%dx)).  Handling
migration of a fully variable sized hunk is not that simple.

Also preventing the guest from accessing outside of the defined
memory does increase the complexity.

Your description of HVM_PARAM_VMPORT_RESET_TIME suggests they aren't
typically accessed very frequently.

The rate I have seen is a low number per minute.  However there
is nothing that prevents a guest from doing a very high rate.

    -Don Slutz


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