From: Paul Durrant pdurrant@amazon.com
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@amazon.com Reviewed-by: David Woodhouse dwmw@amazon.co.uk --- Cc: David Woodhouse dwmw2@infradead.org Cc: Sean Christopherson seanjc@google.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: Borislav Petkov bp@alien8.de Cc: Dave Hansen dave.hansen@linux.intel.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: x86@kernel.org
v8: - Update commit comment.
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 9168a6ec88fd..972098ec4f6a 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1797,9 +1797,6 @@ 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;