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Re: [Xen-devel] [PATCH v2 2/5] vm_event: Implement ARM SMC events

On 04/05/2016 14:30, Razvan Cojocaru wrote:
On 05/04/2016 04:26 PM, Julien Grall wrote:
I may misunderstand some parts of the vm event subsystem. To get/set the
full set of registers, the user will have to use the
DOMCTL_{set,get}vcpucontext, correct? So why does Xen expose a part of
the vCPU context through the vm_event?

Because DOMCTL_{set,get}vcpucontext is expensive, and a serious
introspection application will receive hundreds or thousands of events
per second.

Having what's most commonly needed being sent with the vm_event
eliminates the need for extra hypercalls and can make the difference
between a responsive and an unusable userspace introspection application.

Thank you for the explanation. So in this case, we should also make x16 (AArch64) and r12 (AArch32) available as they will be used for hypercall.


Julien Grall

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