On Tue, 2023-11-21 at 18:02 +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) there > needs to be 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). > > 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, stop considering an inactive vcpu_info > cache as a hard error in kvm_xen_set_evtchn_fast(). > > Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx> > Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx> Wait, didn't we realise that this leaves the bits set in the shadow evtchn_pending_sel that get lost on migration? The point in your previous patch which split out a shiny new set_shinfo_evtchn_pending() function was that you could then *call* that function to ensure that the corresponding index bit was set on the destination host after migration, if the bit in the shinfo is. So we'd do that from kvm_xen_setup_evtchn(), kvm_xen_eventfd_assign(), and when setting KVM_XEN_VCPU_ATTR_TYPE_TIMER. if (bit_is_set_in_shinfo) set_shinfo_evtchn_pending()
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