Index: sys/amd64/amd64/initcpu.c
===================================================================
--- sys/amd64/amd64/initcpu.c
+++ sys/amd64/amd64/initcpu.c
@@ -58,6 +58,7 @@
 static void
 init_amd(void)
 {
+	uint64_t msr;
 
 	/*
 	 * Work around Erratum 721 for Family 10h and 12h processors.
@@ -80,6 +81,20 @@
 			wrmsr(0xc0011029, rdmsr(0xc0011029) | 1);
 		break;
 	}
+
+	/*
+	 * BIOS may configure Family 10h processors to convert WC+ cache type
+	 * to CD.  That can hurt performance of guest VMs using nested paging.
+	 * The relevant MSR bit is not documented in the BKDG,
+	 * the fix is borrowed from Linux.
+	 */
+	if (CPUID_TO_FAMILY(cpu_id) == 0x10) {
+		if ((cpu_feature2 & CPUID2_HV) == 0) {
+			msr = rdmsr(0xc001102a);
+			msr &= ~((uint64_t)1 << 24);
+			wrmsr(0xc001102a, msr);
+		}
+	}
 }
 
 /*