diff --git a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/processor.h b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/processor.h
index 96093ba4bf..5b8d8be639 100644
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/processor.h
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/processor.h
@@ -237,20 +237,11 @@ extern unsigned long mmu_cr4_features;
 
 static inline void set_in_cr4 (unsigned long mask)
 {
+	unsigned cr4;
 	mmu_cr4_features |= mask;
-	switch (mask) {
-	case X86_CR4_OSFXSR:
-	case X86_CR4_OSXMMEXCPT:
-		break;
-	default:
-		do {
-			const char *msg = "Xen unsupported cr4 update\n";
-			(void)HYPERVISOR_console_io(
-				CONSOLEIO_write, __builtin_strlen(msg),
-				(char *)msg);
-			BUG();
-		} while (0);
-	}
+	cr4 = read_cr4();
+	cr4 |= mask;
+	write_cr4(cr4);
 }
 
 static inline void clear_in_cr4 (unsigned long mask)
diff --git a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/processor.h b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/processor.h
index 6fe7ccd450..e000547f62 100644
--- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/processor.h
+++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/processor.h
@@ -141,31 +141,21 @@ extern unsigned long mmu_cr4_features;
 static inline void set_in_cr4 (unsigned long mask)
 {
 	mmu_cr4_features |= mask;
-	switch (mask) {
-	case X86_CR4_OSFXSR:
-	case X86_CR4_OSXMMEXCPT:
-		break;
-	default:
-		do {
-			const char *msg = "Xen unsupported cr4 update\n";
-			(void)HYPERVISOR_console_io(
-				CONSOLEIO_write, __builtin_strlen(msg),
-				(char *)msg);
-			BUG();
-		} while (0);
-	}
+	__asm__("movq %%cr4,%%rax\n\t"
+		"orq %0,%%rax\n\t"
+		"movq %%rax,%%cr4\n"
+		: : "irg" (mask)
+		:"ax");
 }
 
 static inline void clear_in_cr4 (unsigned long mask)
 {
-#ifndef CONFIG_XEN
 	mmu_cr4_features &= ~mask;
 	__asm__("movq %%cr4,%%rax\n\t"
 		"andq %0,%%rax\n\t"
 		"movq %%rax,%%cr4\n"
 		: : "irg" (~mask)
 		:"ax");
-#endif
 }