Index: amd64/amd64/fpu.c
===================================================================
--- amd64/amd64/fpu.c	(revision 266123)
+++ amd64/amd64/fpu.c	(working copy)
@@ -199,6 +199,10 @@
 	TUNABLE_ULONG_FETCH("hw.xsave_mask", &xsave_mask_user);
 	xsave_mask_user |= XFEATURE_ENABLED_X87 | XFEATURE_ENABLED_SSE;
 	xsave_mask &= xsave_mask_user;
+	if ((xsave_mask & XFEATURE_AVX512) != XFEATURE_AVX512)
+		xsave_mask &= ~XFEATURE_AVX512;
+	if ((xsave_mask & XFEATURE_MPX) != XFEATURE_MPX)
+		xsave_mask &= ~XFEATURE_MPX;
 
 	cpuid_count(0xd, 0x1, cp);
 	if ((cp[0] & CPUID_EXTSTATE_XSAVEOPT) != 0) {