On Tue, 2023-09-26 at 12:20 +0000, Paul Durrant wrote: > From: Paul Durrant <pdurrant@xxxxxxxxxx> > > If the guest sets an explicit vcpu_info GPA then, for any of the first 32 > vCPUs, the content of the default vcpu_info in the shared_info page must be > copied into the new location. Because this copy may race with event > delivery (which updates the 'evtchn_pending_sel' field in vcpu_info) we > need a way to defer that until the copy is complete. > Happily there is already a shadow of 'evtchn_pending_sel' in kvm_vcpu_xen > that is used in atomic context if the vcpu_info PFN cache has been > invalidated so that the update of vcpu_info can be deferred until the > cache can be refreshed (on vCPU thread's the way back into guest context). > So let's also use this shadow if the vcpu_info cache has been > *deactivated*, so that the VMM can safely copy the vcpu_info content and > then re-activate the cache with the new GPA. To do this, all we need to do > is stop considering an inactive vcpu_info cache as a hard error in > kvm_xen_set_evtchn_fast(). Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
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