[PATCH v2] x86/HVM: limit upcall vector related verbosity

[Jan Beulich <jbeulich@suse.com>]

Avoid logging all-identical messages for every vCPU, but make sure to
log unusual events like the vector differing from vCPU 0's (note that
the respective condition also makes sure vCPU 0 itself will have the
vector setting logged), or it changing after it was once set. (Arguably
a downside is that some vCPU not having its vector set would no longer
be recognizable from the logs. But I think that's tolerable as
sufficiently unlikely outside of people actively fiddling with related
code.)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v2: Add comment.

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4129,7 +4129,15 @@ static int hvmop_set_evtchn_upcall_vecto
     if ( (v = domain_vcpu(d, op.vcpu)) == NULL )
         return -ENOENT;
 
-    printk(XENLOG_G_INFO "%pv: upcall vector %02x\n", v, op.vector);
+    /*
+     * Avoid logging all-identical messages for every vCPU, but make sure to
+     * log unusual events like the vector differing from vCPU 0's, or it
+     * changing after it was once set
+     */
+    if ( op.vector != d->vcpu[0]->arch.hvm.evtchn_upcall_vector ||
+         (v->arch.hvm.evtchn_upcall_vector &&
+          op.vector != v->arch.hvm.evtchn_upcall_vector) )
+        printk(XENLOG_G_INFO "%pv: upcall vector %02x\n", v, op.vector);
 
     v->arch.hvm.evtchn_upcall_vector = op.vector;
     hvm_assert_evtchn_irq(v);