Re: [Xen-devel] [XEN PATCH v4] x86/vm_event: add short-circuit for breakpoints (aka "fast single step")

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Dec 19, 2019 at 8:47 AM Sergey Kovalev <valor@xxxxxxx> wrote:
>
> When using DRAKVUF (or another system using altp2m with shadow pages similar
> to what is described in
> https://xenproject.org/2016/04/13/stealthy-monitoring-with-xen-altp2m),
> after a breakpoint is hit the system switches to the default
> unrestricted altp2m view with singlestep enabled. When the singlestep
> traps to Xen another vm_event is sent to the monitor agent, which then
> normally disables singlestepping and switches the altp2m view back to
> the restricted view.
>
> This patch short-circuiting that last part so that it doesn't need to send the
> vm_event out for the singlestep event and should switch back to the restricted
> view in Xen automatically.
>
> This optimization gains about 35% speed-up.
>
> Was tested on Debian branch of Xen 4.12. See at:
> https://github.com/skvl/xen/tree/debian/knorrie/4.12/fast-singlestep
>
> Rebased on master:
> https://github.com/skvl/xen/tree/fast-singlestep
>
> Signed-off-by: Sergey Kovalev <valor@xxxxxxx>

Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

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