diff --git a/alioth/src/arch/x86_64/msr.rs b/alioth/src/arch/x86_64/msr.rs
index 61e37a7b..c21a6e38 100644
--- a/alioth/src/arch/x86_64/msr.rs
+++ b/alioth/src/arch/x86_64/msr.rs
@@ -14,22 +14,28 @@
 
 use bitfield::bitfield;
 
-use crate::bitflags;
+use crate::{bitflags, consts};
 
 // Intel Vol.4, Table 2-2.
-pub const IA32_EFER: u32 = 0xc000_0080;
-pub const IA32_STAR: u32 = 0xc000_0081;
-pub const IA32_LSTAR: u32 = 0xc000_0082;
-pub const IA32_CSTAR: u32 = 0xc000_0083;
-pub const IA32_FMASK: u32 = 0xc000_0084;
-pub const IA32_FS_BASE: u32 = 0xc000_0100;
-pub const IA32_GS_BASE: u32 = 0xc000_0101;
-pub const IA32_KERNEL_GS_BASE: u32 = 0xc000_0102;
-pub const IA32_TSC_AUX: u32 = 0xc000_0103;
-pub const IA32_MISC_ENABLE: u32 = 0x0000_01a0;
+consts! {
+    pub struct Msr(u32) {
+        EFER = 0xc000_0080;
+        STAR = 0xc000_0081;
+        LSTAR = 0xc000_0082;
+        CSTAR = 0xc000_0083;
+        FMASK = 0xc000_0084;
+        FS_BASE = 0xc000_0100;
+        GS_BASE = 0xc000_0101;
+        KERNEL_GS_BASE = 0xc000_0102;
+        TSC_AUX = 0xc000_0103;
+        MISC_ENABLE = 0x0000_01a0;
+        APIC_BASE = 0x0000_001b;
+    }
+}
 
 bitflags! {
-    pub struct Efer(u32) {
+    #[derive(Default)]
+    pub struct Efer(u64) {
         /// SYSCALL enable
         SCE = 1 << 0;
         /// IA-32e mode enable
diff --git a/alioth/src/arch/x86_64/reg.rs b/alioth/src/arch/x86_64/reg.rs
index e167bfe2..b72b1ff3 100644
--- a/alioth/src/arch/x86_64/reg.rs
+++ b/alioth/src/arch/x86_64/reg.rs
@@ -58,7 +58,8 @@ bitflags! {
 }
 
 bitflags! {
-    pub struct Cr0(u32) {
+    #[derive(Default)]
+    pub struct Cr0(u64) {
         /// CarryProtected Mode Enable
         PE = 1 << 0;
         /// CarryMonitor co-processor
@@ -85,6 +86,7 @@ bitflags! {
 }
 
 bitflags! {
+    #[derive(Default)]
     pub struct Cr3(u64) {
         /// CarryPage-level write-through
         PWT = 1 << 3;
@@ -94,7 +96,8 @@ bitflags! {
 }
 
 bitflags! {
-    pub struct Cr4(u32) {
+    #[derive(Default)]
+    pub struct Cr4(u64) {
         /// CarryVirtual 8086 Mode Extensions
         VME = 1 << 0;
         /// CarryProtected-mode Virtual Interrupts
@@ -195,8 +198,6 @@ pub enum SReg {
     Cr3,
     Cr4,
     Cr8,
-    Efer,
-    ApicBase,
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
diff --git a/alioth/src/board/board_x86_64/board_x86_64.rs b/alioth/src/board/board_x86_64/board_x86_64.rs
index 521e4396..385f525e 100644
--- a/alioth/src/board/board_x86_64/board_x86_64.rs
+++ b/alioth/src/board/board_x86_64/board_x86_64.rs
@@ -31,7 +31,7 @@ use crate::arch::layout::{
     BIOS_DATA_END, EBDA_END, EBDA_START, IOAPIC_START, MEM_64_START, PORT_ACPI_RESET,
     PORT_ACPI_SLEEP_CONTROL, PORT_ACPI_TIMER, RAM_32_SIZE,
 };
-use crate::arch::msr::{IA32_MISC_ENABLE, MiscEnable};
+use crate::arch::msr::{MiscEnable, Msr};
 use crate::board::{Board, BoardConfig, CpuTopology, PCIE_MMIO_64_SIZE, Result, VcpuGuard, error};
 use crate::device::ioapic::IoApic;
 use crate::firmware::acpi::bindings::{
@@ -241,6 +241,7 @@ where
             return Ok(());
         }
         vcpu.set_sregs(&init_state.sregs, &init_state.seg_regs, &init_state.dt_regs)?;
+        vcpu.set_msrs(&init_state.msrs)?;
         vcpu.set_regs(&init_state.regs)?;
         Ok(())
     }
@@ -257,7 +258,7 @@ where
             }
         }
         vcpu.set_cpuids(cpuids)?;
-        vcpu.set_msrs(&[(IA32_MISC_ENABLE, MiscEnable::FAST_STRINGS.bits())])?;
+        vcpu.set_msrs(&[(Msr::MISC_ENABLE, MiscEnable::FAST_STRINGS.bits())])?;
         Ok(())
     }
 
diff --git a/alioth/src/hv/hv.rs b/alioth/src/hv/hv.rs
index 0958e51f..741f1658 100644
--- a/alioth/src/hv/hv.rs
+++ b/alioth/src/hv/hv.rs
@@ -35,6 +35,8 @@ use snafu::{AsErrorSource, Snafu};
 #[cfg(target_arch = "x86_64")]
 use crate::arch::cpuid::CpuidIn;
 #[cfg(target_arch = "x86_64")]
+use crate::arch::msr::Msr;
+#[cfg(target_arch = "x86_64")]
 use crate::arch::reg::{DtReg, DtRegVal, SegReg, SegRegVal};
 use crate::arch::reg::{Reg, SReg};
 #[cfg(target_arch = "x86_64")]
@@ -207,7 +209,7 @@ pub trait Vcpu {
     fn set_cpuids(&mut self, cpuids: HashMap<CpuidIn, CpuidResult>) -> Result<(), Error>;
 
     #[cfg(target_arch = "x86_64")]
-    fn set_msrs(&mut self, msrs: &[(u32, u64)]) -> Result<()>;
+    fn set_msrs(&mut self, msrs: &[(Msr, u64)]) -> Result<()>;
 
     fn dump(&self) -> Result<(), Error>;
 
diff --git a/alioth/src/hv/kvm/vcpu/vcpu.rs b/alioth/src/hv/kvm/vcpu/vcpu.rs
index 07de7090..4c80509e 100644
--- a/alioth/src/hv/kvm/vcpu/vcpu.rs
+++ b/alioth/src/hv/kvm/vcpu/vcpu.rs
@@ -37,6 +37,8 @@ use snafu::ResultExt;
 #[cfg(target_arch = "x86_64")]
 use crate::arch::cpuid::CpuidIn;
 #[cfg(target_arch = "x86_64")]
+use crate::arch::msr::Msr;
+#[cfg(target_arch = "x86_64")]
 use crate::arch::reg::{DtReg, DtRegVal, SegReg, SegRegVal};
 use crate::arch::reg::{Reg, SReg};
 use crate::ffi;
@@ -227,7 +229,7 @@ impl Vcpu for KvmVcpu {
     }
 
     #[cfg(target_arch = "x86_64")]
-    fn set_msrs(&mut self, msrs: &[(u32, u64)]) -> Result<()> {
+    fn set_msrs(&mut self, msrs: &[(Msr, u64)]) -> Result<()> {
         self.kvm_set_msrs(msrs)
     }
 
diff --git a/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64.rs b/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64.rs
index 9f34c927..12100062 100644
--- a/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64.rs
+++ b/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64.rs
@@ -22,7 +22,8 @@ use std::os::fd::{FromRawFd, OwnedFd};
 use snafu::ResultExt;
 
 use crate::arch::cpuid::CpuidIn;
-use crate::arch::reg::{DtReg, DtRegVal, Reg, SReg, SegAccess, SegReg, SegRegVal};
+use crate::arch::msr::{Efer, Msr};
+use crate::arch::reg::{Cr0, Cr3, Cr4, DtReg, DtRegVal, Reg, SReg, SegAccess, SegReg, SegRegVal};
 use crate::hv::kvm::kvm_error;
 use crate::hv::kvm::vcpu::KvmVcpu;
 use crate::hv::kvm::vm::KvmVm;
@@ -47,13 +48,11 @@ impl VcpuArch {
 macro_rules! set_kvm_sreg {
     ($kvm_sregs:ident, $sreg:ident, $val:expr) => {
         match $sreg {
-            SReg::Cr0 => $kvm_sregs.cr0 = $val,
+            SReg::Cr0 => $kvm_sregs.cr0 = Cr0::from_bits_retain($val),
             SReg::Cr2 => $kvm_sregs.cr2 = $val,
-            SReg::Cr3 => $kvm_sregs.cr3 = $val,
-            SReg::Cr4 => $kvm_sregs.cr4 = $val,
+            SReg::Cr3 => $kvm_sregs.cr3 = Cr3::from_bits_retain($val),
+            SReg::Cr4 => $kvm_sregs.cr4 = Cr4::from_bits_retain($val),
             SReg::Cr8 => $kvm_sregs.cr8 = $val,
-            SReg::Efer => $kvm_sregs.efer = $val,
-            SReg::ApicBase => $kvm_sregs.apic_base = $val,
         }
     };
 }
@@ -99,13 +98,21 @@ macro_rules! set_kvm_seg_reg {
 macro_rules! get_kvm_sreg {
     ($kvm_sregs:ident, $sreg:ident) => {
         match $sreg {
-            SReg::Cr0 => $kvm_sregs.cr0,
+            SReg::Cr0 => $kvm_sregs.cr0.bits(),
             SReg::Cr2 => $kvm_sregs.cr2,
-            SReg::Cr3 => $kvm_sregs.cr3,
-            SReg::Cr4 => $kvm_sregs.cr4,
+            SReg::Cr3 => $kvm_sregs.cr3.bits(),
+            SReg::Cr4 => $kvm_sregs.cr4.bits(),
             SReg::Cr8 => $kvm_sregs.cr8,
-            SReg::Efer => $kvm_sregs.efer,
-            SReg::ApicBase => $kvm_sregs.apic_base,
+        }
+    };
+}
+
+macro_rules! fix_kvm_efer {
+    ($kvm_sregs:ident) => {
+        if $kvm_sregs.cr0.contains(Cr0::PG) && $kvm_sregs.cr4.contains(Cr4::PAE) {
+            $kvm_sregs.efer |= Efer::LME | Efer::LMA;
+        } else {
+            $kvm_sregs.efer &= !(Efer::LME | Efer::LMA);
         }
     };
 }
@@ -243,6 +250,7 @@ impl KvmVcpu {
         for (reg, val) in seg_regs {
             set_kvm_seg_reg!(kvm_sregs2, reg, val);
         }
+        fix_kvm_efer!(kvm_sregs2);
         unsafe { kvm_set_sregs2(&self.fd, &kvm_sregs2) }.context(error::VcpuReg)?;
         Ok(())
     }
@@ -281,6 +289,7 @@ impl KvmVcpu {
         for (reg, val) in seg_regs {
             set_kvm_seg_reg!(kvm_sregs, reg, val);
         }
+        fix_kvm_efer!(kvm_sregs);
         unsafe { kvm_set_sregs(&self.fd, &kvm_sregs) }.context(error::VcpuReg)?;
         Ok(())
     }
@@ -329,14 +338,14 @@ impl KvmVcpu {
         Ok(())
     }
 
-    pub fn kvm_set_msrs(&mut self, msrs: &[(u32, u64)]) -> Result<()> {
+    pub fn kvm_set_msrs(&mut self, msrs: &[(Msr, u64)]) -> Result<()> {
         let mut kvm_msrs = KvmMsrs {
             nmsrs: msrs.len() as u32,
             _pad: 0,
             entries: [KvmMsrEntry::default(); MAX_IO_MSRS],
         };
         for (i, (index, data)) in msrs.iter().enumerate() {
-            kvm_msrs.entries[i].index = *index;
+            kvm_msrs.entries[i].index = index.raw();
             kvm_msrs.entries[i].data = *data;
         }
         unsafe { kvm_set_msrs(&self.fd, &kvm_msrs) }.context(error::GuestMsr)?;
diff --git a/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64_test.rs b/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64_test.rs
index 8407debf..ec773c70 100644
--- a/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64_test.rs
+++ b/alioth/src/hv/kvm/vcpu/vcpu_x86_64/vcpu_x86_64_test.rs
@@ -18,7 +18,7 @@ use std::ptr::null_mut;
 use assert_matches::assert_matches;
 use libc::{MAP_ANONYMOUS, MAP_FAILED, MAP_SHARED, PROT_EXEC, PROT_READ, PROT_WRITE, mmap};
 
-use crate::arch::msr::Efer;
+use crate::arch::msr::{Efer, Msr};
 use crate::arch::paging::Entry;
 use crate::arch::reg::{Cr0, Cr4, Reg, SegAccess};
 use crate::ffi;
@@ -68,8 +68,6 @@ fn test_vcpu_regs() {
         (SReg::Cr3, 0x1362d001),
         (SReg::Cr4, 1 << 5),
         (SReg::Cr8, 0x0),
-        (SReg::Efer, (1 << 8) | (1 << 10)),
-        (SReg::ApicBase, 0xfee00900),
     ];
     let seg_regs = [
         (
@@ -280,10 +278,9 @@ fn test_kvm_run() {
     let idtr = DtRegVal { base: 0, limit: 0 };
     vcpu.set_sregs(
         &[
-            (SReg::Efer, (Efer::LMA | Efer::LME).bits() as u64),
-            (SReg::Cr0, (Cr0::NE | Cr0::PE | Cr0::PG).bits() as u64),
+            (SReg::Cr0, (Cr0::NE | Cr0::PE | Cr0::PG).bits()),
             (SReg::Cr3, 0x2000),
-            (SReg::Cr4, Cr4::PAE.bits() as u64),
+            (SReg::Cr4, Cr4::PAE.bits()),
         ],
         &[
             (SegReg::Cs, cs),
@@ -298,6 +295,8 @@ fn test_kvm_run() {
         &[(DtReg::Gdtr, gdtr), (DtReg::Idtr, idtr)],
     )
     .unwrap();
+    vcpu.set_msrs(&[(Msr::EFER, (Efer::LMA | Efer::LME).bits())])
+        .unwrap();
     vcpu.set_regs(&[
         (Reg::Rip, 0x1000),
         (Reg::Rax, 0x2),
diff --git a/alioth/src/loader/firmware/firmware_x86_64.rs b/alioth/src/loader/firmware/firmware_x86_64.rs
index e4523b14..2f34eeaf 100644
--- a/alioth/src/loader/firmware/firmware_x86_64.rs
+++ b/alioth/src/loader/firmware/firmware_x86_64.rs
@@ -20,6 +20,7 @@ use std::sync::Arc;
 use snafu::ResultExt;
 
 use crate::arch::layout::MEM_64_START;
+use crate::arch::msr::Msr;
 use crate::arch::reg::{Cr0, DtReg, DtRegVal, Reg, Rflags, SReg, SegAccess, SegReg, SegRegVal};
 use crate::loader::{InitState, Result, error};
 use crate::mem::mapped::ArcMemPages;
@@ -98,13 +99,13 @@ pub fn load<P: AsRef<Path>>(memory: &Memory, path: P) -> Result<(InitState, ArcM
             (Reg::Rflags, Rflags::RESERVED_1.bits() as u64),
         ],
         sregs: vec![
-            (SReg::Cr0, (Cr0::ET | Cr0::NW | Cr0::CD).bits() as u64),
+            (SReg::Cr0, (Cr0::ET | Cr0::NW | Cr0::CD).bits()),
             (SReg::Cr2, 0),
             (SReg::Cr3, 0),
             (SReg::Cr4, 0),
             (SReg::Cr8, 0),
-            (SReg::Efer, 0),
         ],
+        msrs: vec![(Msr::EFER, 0)],
         seg_regs: vec![
             (SegReg::Cs, boot_cs),
             (SegReg::Ds, boot_ds),
diff --git a/alioth/src/loader/linux/linux_x86_64.rs b/alioth/src/loader/linux/linux_x86_64.rs
index ae028713..982ef7df 100644
--- a/alioth/src/loader/linux/linux_x86_64.rs
+++ b/alioth/src/loader/linux/linux_x86_64.rs
@@ -25,7 +25,7 @@ use crate::arch::layout::{
     APIC_START, BOOT_GDT_START, BOOT_PAGING_START, EBDA_START, KERNEL_CMDLINE_LIMIT,
     KERNEL_CMDLINE_START, KERNEL_IMAGE_START, LINUX_BOOT_PARAMS_START,
 };
-use crate::arch::msr::{ApicBase, Efer};
+use crate::arch::msr::{ApicBase, Efer, Msr};
 use crate::arch::paging::Entry;
 use crate::arch::reg::{
     Cr0, Cr4, DtReg, DtRegVal, Reg, Rflags, SReg, SegAccess, SegReg, SegRegVal,
@@ -251,11 +251,9 @@ pub fn load<P: AsRef<Path>>(
             (Reg::Rflags, Rflags::RESERVED_1.bits() as u64),
         ],
         sregs: vec![
-            (SReg::Efer, (Efer::LMA | Efer::LME).bits() as u64),
-            (SReg::Cr0, (Cr0::NE | Cr0::PE | Cr0::PG).bits() as u64),
+            (SReg::Cr0, (Cr0::NE | Cr0::PE | Cr0::PG).bits()),
             (SReg::Cr3, pml4_start),
-            (SReg::Cr4, Cr4::PAE.bits() as u64),
-            (SReg::ApicBase, apic_base.0),
+            (SReg::Cr4, Cr4::PAE.bits()),
         ],
         seg_regs: vec![
             (SegReg::Cs, boot_cs),
@@ -268,6 +266,10 @@ pub fn load<P: AsRef<Path>>(
             (SegReg::Ldtr, boot_ldtr),
         ],
         dt_regs: vec![(DtReg::Gdtr, gdtr), (DtReg::Idtr, idtr)],
+        msrs: vec![
+            (Msr::EFER, (Efer::LMA | Efer::LME).bits()),
+            (Msr::APIC_BASE, apic_base.0),
+        ],
         initramfs: initramfs_range,
     })
 }
diff --git a/alioth/src/loader/loader.rs b/alioth/src/loader/loader.rs
index 3d87c3bc..bfdb753e 100644
--- a/alioth/src/loader/loader.rs
+++ b/alioth/src/loader/loader.rs
@@ -28,6 +28,8 @@ use std::path::Path;
 use serde::Deserialize;
 use snafu::Snafu;
 
+#[cfg(target_arch = "x86_64")]
+use crate::arch::msr::Msr;
 #[cfg(target_arch = "x86_64")]
 use crate::arch::reg::{DtReg, DtRegVal, SegReg, SegRegVal};
 use crate::arch::reg::{Reg, SReg};
@@ -57,6 +59,8 @@ pub struct InitState {
     pub dt_regs: Vec<(DtReg, DtRegVal)>,
     #[cfg(target_arch = "x86_64")]
     pub seg_regs: Vec<(SegReg, SegRegVal)>,
+    #[cfg(target_arch = "x86_64")]
+    pub msrs: Vec<(Msr, u64)>,
     pub initramfs: Option<Range<u64>>,
 }
 
diff --git a/alioth/src/loader/xen/xen.rs b/alioth/src/loader/xen/xen.rs
index e0ff14f5..00802b05 100644
--- a/alioth/src/loader/xen/xen.rs
+++ b/alioth/src/loader/xen/xen.rs
@@ -28,7 +28,7 @@ use crate::arch::layout::{
     APIC_START, BOOT_GDT_START, EBDA_START, HVM_START_INFO_START, KERNEL_CMDLINE_LIMIT,
     KERNEL_CMDLINE_START,
 };
-use crate::arch::msr::ApicBase;
+use crate::arch::msr::{ApicBase, Msr};
 use crate::arch::reg::{Cr0, DtReg, DtRegVal, Reg, Rflags, SReg, SegAccess, SegReg, SegRegVal};
 use crate::loader::elf::{
     ELF_HEADER_MAGIC, ELF_IDENT_CLASS_64, ELF_IDENT_LITTLE_ENDIAN, Elf64Header, Elf64Note,
@@ -317,12 +317,7 @@ pub fn load<P: AsRef<Path>>(
             (Reg::Rflags, Rflags::RESERVED_1.bits() as u64),
             (Reg::Rip, entry_point),
         ],
-        sregs: vec![
-            (SReg::Cr0, Cr0::PE.bits() as u64),
-            (SReg::Cr4, 0),
-            (SReg::Efer, 0),
-            (SReg::ApicBase, apic_base.0),
-        ],
+        sregs: vec![(SReg::Cr0, Cr0::PE.bits()), (SReg::Cr4, 0)],
         seg_regs: vec![
             (SegReg::Cs, boot_cs),
             (SegReg::Ds, boot_ds),
@@ -334,6 +329,7 @@ pub fn load<P: AsRef<Path>>(
             (SegReg::Ldtr, boot_ldtr),
         ],
         dt_regs: vec![(DtReg::Gdtr, gdtr), (DtReg::Idtr, idtr)],
+        msrs: vec![(Msr::APIC_BASE, apic_base.0), (Msr::EFER, 0)],
         initramfs: initramfs_range,
     })
 }
diff --git a/alioth/src/sys/linux/kvm.rs b/alioth/src/sys/linux/kvm.rs
index 74debad0..680efb1e 100644
--- a/alioth/src/sys/linux/kvm.rs
+++ b/alioth/src/sys/linux/kvm.rs
@@ -16,6 +16,8 @@ use std::fmt::{Debug, Formatter, Result};
 
 use bitfield::bitfield;
 
+use crate::arch::x86_64::msr::{ApicBase, Efer};
+use crate::arch::x86_64::reg::{Cr0, Cr3, Cr4};
 use crate::sys::ioctl::{ioctl_ior, ioctl_iowr};
 use crate::{
     bitflags, consts, ioctl_none, ioctl_read, ioctl_write_buf, ioctl_write_ptr, ioctl_write_val,
@@ -231,13 +233,13 @@ pub struct KvmSregs {
     pub ldt: KvmSegment,
     pub gdt: KvmDtable,
     pub idt: KvmDtable,
-    pub cr0: u64,
+    pub cr0: Cr0,
     pub cr2: u64,
-    pub cr3: u64,
-    pub cr4: u64,
+    pub cr3: Cr3,
+    pub cr4: Cr4,
     pub cr8: u64,
-    pub efer: u64,
-    pub apic_base: u64,
+    pub efer: Efer,
+    pub apic_base: ApicBase,
     pub interrupt_bitmap: [u64; 4],
 }
 
@@ -254,13 +256,13 @@ pub struct KvmSregs2 {
     pub ldt: KvmSegment,
     pub gdt: KvmDtable,
     pub idt: KvmDtable,
-    pub cr0: u64,
+    pub cr0: Cr0,
     pub cr2: u64,
-    pub cr3: u64,
-    pub cr4: u64,
+    pub cr3: Cr3,
+    pub cr4: Cr4,
     pub cr8: u64,
-    pub efer: u64,
-    pub apic_base: u64,
+    pub efer: Efer,
+    pub apic_base: ApicBase,
     pub flags: u64,
     pub pdptrs: [u64; 4],
 }