fix(x86_64): specify IA32_MTRRdefType MSR on boot

CHANGELOG.md

@@ -19,6 +19,9 @@ and this project adheres to
 - [#4028](https://github.com/firecracker-microvm/firecracker/pull/4028):
   Firecracker now creates the log and metrics files if they do not exist,
   simplifying the launch of Firecracker by removing a manual step.
+- [#5526](https://github.com/firecracker-microvm/firecracker/pull/5526): Specify
+  IA32_MTRRdefType MSR on VM boot to allow it to set page attributes for memory
+  regions.
 
 ### Deprecated
 

src/vmm/src/arch/x86_64/msr.rs

@@ -419,6 +419,15 @@ pub fn create_boot_msr_entries() -> Vec<kvm_msr_entry> {
             data: u64::from(MSR_IA32_MISC_ENABLE_FAST_STRING),
             ..Default::default()
         },
+        // set default memory type for physical memory outside configured
+        // memory ranges to write-back by setting MTRR enable bit (11) and
+        // setting memory type to write-back (value 6).
+        // https://wiki.osdev.org/MTRR
+        kvm_msr_entry {
+            index: MSR_MTRRdefType,
+            data: (1 << 11) | 0x6,
+            ..Default::default()
+        },
     ]
 }
 

src/vmm/src/cpu_config/x86_64/cpuid/common.rs

@@ -2,6 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0
 #![allow(clippy::restriction)]
 
+use crate::arch::x86_64::generated::msr_index::{
+    MSR_IA32_BNDCFGS, MSR_IA32_CR_PAT, MSR_MTRRdefType, MSR_MTRRfix4K_C0000, MSR_MTRRfix4K_C8000,
+    MSR_MTRRfix4K_D0000, MSR_MTRRfix4K_D8000, MSR_MTRRfix4K_E0000, MSR_MTRRfix4K_E8000,
+    MSR_MTRRfix4K_F0000, MSR_MTRRfix4K_F8000, MSR_MTRRfix16K_80000, MSR_MTRRfix16K_A0000,
+    MSR_MTRRfix64K_00000,
+};
+
 /// Error type for [`get_cpuid`].
 #[derive(Debug, thiserror::Error, displaydoc::Display, PartialEq, Eq)]
 pub enum GetCpuidError {
@@ -93,13 +100,7 @@ pub(crate) fn msrs_to_save_by_cpuid(cpuid: &kvm_bindings::CpuId) -> Vec<u32> {
     }
 
     // TODO: Add more dependencies.
-    cpuid_msr_dep!(
-        0x7,
-        0,
-        ebx,
-        MPX_BITINDEX,
-        [crate::arch::x86_64::generated::msr_index::MSR_IA32_BNDCFGS]
-    );
+    cpuid_msr_dep!(0x7, 0, ebx, MPX_BITINDEX, [MSR_IA32_BNDCFGS]);
 
     // IA32_MTRR_PHYSBASEn, IA32_MTRR_PHYSMASKn
     cpuid_msr_dep!(0x1, 0, edx, MTRR_BITINDEX, 0x200..0x210);
@@ -111,19 +112,19 @@ pub(crate) fn msrs_to_save_by_cpuid(cpuid: &kvm_bindings::CpuId) -> Vec<u32> {
         edx,
         MTRR_BITINDEX,
         [
-            0x250, // IA32_MTRR_FIX64K_00000
-            0x258, // IA32_MTRR_FIX16K_80000
-            0x259, // IA32_MTRR_FIX16K_A0000
-            0x268, // IA32_MTRR_FIX4K_C0000
-            0x269, // IA32_MTRR_FIX4K_C8000
-            0x26a, // IA32_MTRR_FIX4K_D0000
-            0x26b, // IA32_MTRR_FIX4K_D8000
-            0x26c, // IA32_MTRR_FIX4K_E0000
-            0x26d, // IA32_MTRR_FIX4K_E8000
-            0x26e, // IA32_MTRR_FIX4K_F0000
-            0x26f, // IA32_MTRR_FIX4K_F8000
-            0x277, // IA32_PAT
-            0x2ff  // IA32_MTRR_DEF_TYPE
+            MSR_MTRRfix64K_00000,
+            MSR_MTRRfix16K_80000,
+            MSR_MTRRfix16K_A0000,
+            MSR_MTRRfix4K_C0000,
+            MSR_MTRRfix4K_C8000,
+            MSR_MTRRfix4K_D0000,
+            MSR_MTRRfix4K_D8000,
+            MSR_MTRRfix4K_E0000,
+            MSR_MTRRfix4K_E8000,
+            MSR_MTRRfix4K_F0000,
+            MSR_MTRRfix4K_F8000,
+            MSR_IA32_CR_PAT,
+            MSR_MTRRdefType,
         ]
     );
 

tests/integration_tests/functional/test_cpu_template_helper.py

@@ -205,6 +205,8 @@ def build_cpu_config_dict(cpu_config_path):
     # features are temporarily disabled. Guest OS disables TILEDATA by default
     # using the MSR.
     0x1C4,
+    # IA32_PAT_MSR is R/W MSR for guest OS to control memory page attributes.
+    0x277,
     # MSR_IA32_TSC_DEADLINE specifies the time at which a timer interrupt
     # should occur and depends on the elapsed time.
     0x6E0,