This patch originally comes from the Linus mainline kernel (2.6.33),
find below the patch details:

From: Andreas Herrmann <herrmann.der.user@xxxxxxxxxxxxxx>
Subject: x86: ucode-amd: Don't warn when no ucode is available for a CPU revision

There is no point in warning when there is no ucode available
for a specific CPU revision. Currently the container-file, which
provides the AMD ucode patches for OS load, contains only a few
ucode patches.

It's already clearly indicated by the printed patch_level
whenever new ucode was available and an update happened. So the
warning message is of no help but rather annoying on systems
with many CPUs.

Signed-off-by: Thomas Renninger <trenn@xxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -96,11 +96,7 @@ static int microcode_fits(void *mc, int 
     }
 
     if ( !equiv_cpu_id )
-    {
-        printk(KERN_ERR "microcode: CPU%d cpu_id "
-               "not found in equivalent cpu table\n", cpu);
-        return -EINVAL;
-    }
+	    return 0;
 
     if ( (mc_header->processor_rev_id) != equiv_cpu_id )
     {