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(). Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx> Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx> --- Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx> Cc: Sean Christopherson <seanjc@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: x86@xxxxxxxxxx v6: - New in this version. --- arch/x86/kvm/xen.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index aafc794940e4..e645066217bb 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1606,9 +1606,6 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm) WRITE_ONCE(xe->vcpu_idx, vcpu->vcpu_idx); } - if (!vcpu->arch.xen.vcpu_info_cache.active) - return -EINVAL; - if (xe->port >= max_evtchn_port(kvm)) return -EINVAL; -- 2.39.2
