diff --git a/sys/dev/hwpmc/hwpmc_intel.c b/sys/dev/hwpmc/hwpmc_intel.c
--- a/sys/dev/hwpmc/hwpmc_intel.c
+++ b/sys/dev/hwpmc/hwpmc_intel.c
@@ -149,7 +149,7 @@
 			break;
 		case 0x2A:	/* Per Intel document 253669-039US 05/2011. */
 			cputype = PMC_CPU_INTEL_SANDYBRIDGE;
-			nclasses = 5;
+			nclasses = 3;
 			break;
 		case 0x2D:	/* Per Intel document 253669-044US 08/2012. */
 			cputype = PMC_CPU_INTEL_SANDYBRIDGE_XEON;
@@ -195,7 +195,7 @@
 		case 0x3C:	/* Per Intel document 325462-045US 01/2013. */
 		case 0x45:	/* Per Intel document 325462-045US 09/2014. */
 			cputype = PMC_CPU_INTEL_HASWELL;
-			nclasses = 5;
+			nclasses = 3;
 			break;
 		case 0x37:
 		case 0x4A:
@@ -275,10 +275,27 @@
 		 * Intel Corei7 and Westmere processors.
 		 */
 	case PMC_CPU_INTEL_COREI7:
-	case PMC_CPU_INTEL_HASWELL:
-	case PMC_CPU_INTEL_SANDYBRIDGE:
 	case PMC_CPU_INTEL_WESTMERE:
+#ifdef notyet
+	/*
+	 * TODO: re-enable uncore class on these processors.
+	 *
+	 * The uncore unit was reworked beginning with Sandy Bridge, including
+	 * the MSRs required to program it. In particular, we need to:
+	 *  - Parse the MSR_UNC_CBO_CONFIG MSR for number of C-box units in the
+	 *    system
+	 *  - Support reading and writing to ARB and C-box units, depending on
+	 *    the requested event
+	 *  - Create some kind of mapping between C-box <--> CPU
+	 *
+	 * Also TODO: support other later changes to these interfaces, to
+	 * enable the uncore class on generations newer than Broadwell.
+	 * Skylake+ appears to use newer addresses for the uncore MSRs.
+	 */
+	case PMC_CPU_INTEL_HASWELL:
 	case PMC_CPU_INTEL_BROADWELL:
+	case PMC_CPU_INTEL_SANDYBRIDGE:
+#endif
 		error = pmc_uncore_initialize(pmc_mdep, ncpus);
 		break;
 	default:
@@ -329,11 +346,13 @@
 	 * Uncore.
 	 */
 	switch (md->pmd_cputype) {
-	case PMC_CPU_INTEL_BROADWELL:
 	case PMC_CPU_INTEL_COREI7:
+	case PMC_CPU_INTEL_WESTMERE:
+#ifdef notyet
 	case PMC_CPU_INTEL_HASWELL:
+	case PMC_CPU_INTEL_BROADWELL:
 	case PMC_CPU_INTEL_SANDYBRIDGE:
-	case PMC_CPU_INTEL_WESTMERE:
+#endif
 		pmc_uncore_finalize(md);
 		break;
 	default: