diff --git a/src/arch/i386/prefix/libprefix.S b/src/arch/i386/prefix/libprefix.S
index 197a86bc..3aee415f 100644
--- a/src/arch/i386/prefix/libprefix.S
+++ b/src/arch/i386/prefix/libprefix.S
@@ -522,8 +522,11 @@ alloc_basemem:
 	subw	$_data16_memsz_pgh, %ax
 	pushw	%ax
 
-	/* Calculate .text16 segment address */
+	/* Calculate .text16 segment address.  Round down to ensure
+	 * low bits are zero, to speed up mode transitions under KVM.
+	 */
 	subw	$_text16_memsz_pgh, %ax
+	andb	$~0x03, %al
 	pushw	%ax
 
 	/* Update FBMS */
diff --git a/src/arch/i386/transitions/librm.S b/src/arch/i386/transitions/librm.S
index 0d8110ac..eaf520b3 100644
--- a/src/arch/i386/transitions/librm.S
+++ b/src/arch/i386/transitions/librm.S
@@ -200,10 +200,22 @@ real_to_prot:
 	addr32 leal (%eax,%edx), %esi
 	subl	rm_virt_offset, %esi
 
+	/* Load protected-mode global descriptor table */
+	data32 lgdt gdtr
+
+	/* Zero segment registers.  This wastes around 12 cycles on
+	 * real hardware, but saves a substantial number of emulated
+	 * instructions under KVM.
+	 */
+	xorw	%ax, %ax
+	movw	%ax, %ds
+	movw	%ax, %es
+	movw	%ax, %fs
+	movw	%ax, %gs
+	movw	%ax, %ss
+
 	/* Switch to protected mode */
 	cli
-	data32 lgdt gdtr
-	data32 lidt idtr
 	movl	%cr0, %eax
 	orb	$CR0_PE, %al
 	movl	%eax, %cr0
@@ -220,6 +232,9 @@ r2p_pmode:
 	movw	%ax, %ss
 	movl	pm_esp, %esp
 
+	/* Load protected-mode interrupt descriptor table */
+	lidt	idtr
+
 	/* Record real-mode %ss:sp (after removal of data) */
 	movw	%bp, rm_ss
 	addl	%ecx, %edx
diff --git a/src/arch/i386/transitions/librm_mgmt.c b/src/arch/i386/transitions/librm_mgmt.c
index dee14357..f90d49b0 100644
--- a/src/arch/i386/transitions/librm_mgmt.c
+++ b/src/arch/i386/transitions/librm_mgmt.c
@@ -26,10 +26,9 @@ static struct interrupt_vector intr_vec[ IRQ_MAX + 1 ];
 struct interrupt_descriptor idt[NUM_INT] __attribute__ (( aligned ( 16 ) ));
 
 /** The interrupt descriptor table register */
-struct idtr __data16 ( idtr ) = {
+struct idtr idtr = {
 	.limit = ( sizeof ( idt ) - 1 ),
 };
-#define idtr __use_data16 ( idtr )
 
 /**
  * Allocate space on the real-mode stack and copy data there from a