vmm: Remove PC from vCPU config dump

The dumped vCPU config is used to: - create a new custom CPU template based on it - keep track of its changes over time. The value of program counter (PC) is determined by the given kernel image, so it should not be overwritten by a custom CPU template and does not need to be tracked as part of a fingerprint file. Signed-off-by: Takahiro Itazuri <[email protected]>
firecracker-microvm · Sep 20, 2023 · a8deede · a8deede
1 parent 3156667
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Showing 8 changed files with 16 additions and 26 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -39,6 +39,9 @@
   if no limit is set). This avoids the kernel reallocating the fdtable during
   Firecracker operations, resulting in a 30ms to 70ms reduction of snapshot
   restore times for medium to large microVMs with many devices attached.
+- Changed the dump feature of `cpu-template-helper` tool not to enumerate program
+  counter (PC) on ARM because it is determined by the given kernel image and
+  it is useless in the custom CPU template context.
 
 ### Fixed
 

diff --git a/src/vmm/src/vstate/vcpu/aarch64.rs b/src/vmm/src/vstate/vcpu/aarch64.rs
@@ -5,14 +5,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the THIRD-PARTY file.
 
+use kvm_bindings::*;
 use kvm_ioctls::*;
 use logger::{error, IncMetric, METRICS};
 use utils::vm_memory::{Address, GuestAddress, GuestMemoryMmap};
 use versionize::{VersionMap, Versionize, VersionizeError, VersionizeResult};
 use versionize_derive::Versionize;
 
 use crate::arch::aarch64::regs::{
-    Aarch64RegisterOld, Aarch64RegisterRef, Aarch64RegisterVec, KVM_REG_ARM_TIMER_CNT,
+    arm64_core_reg_id, offset__of, Aarch64RegisterOld, Aarch64RegisterRef, Aarch64RegisterVec,
+    KVM_REG_ARM_TIMER_CNT,
 };
 use crate::arch::aarch64::vcpu::{
     get_all_registers, get_all_registers_ids, get_mpidr, get_mpstate, get_registers, set_mpstate,
@@ -208,11 +210,20 @@ impl KvmVcpu {
     pub fn dump_cpu_config(&self) -> Result<CpuConfiguration, KvmVcpuError> {
         let mut reg_list = get_all_registers_ids(&self.fd).map_err(KvmVcpuError::DumpCpuConfig)?;
 
+        let kvm_reg_pc = {
+            let kreg_off = offset__of!(kvm_regs, regs);
+            let pc_off = offset__of!(user_pt_regs, pc) + kreg_off;
+            arm64_core_reg_id!(KVM_REG_SIZE_U64, pc_off)
+        };
+
         // KVM_REG_ARM_TIMER_CNT should be removed, because it depends on the elapsed time and
         // the dumped CPU config is used to create custom CPU templates to modify CPU features
         // exposed to guests or ot detect CPU configuration changes caused by firecracker/KVM/
         // BIOS.
-        reg_list.retain(|&reg_id| reg_id != KVM_REG_ARM_TIMER_CNT);
+        // The value of program counter (PC) is determined by the given kernel image. It should not
+        // be overwritten by a custom CPU template and does not need to be tracked in a fingerprint
+        // file.
+        reg_list.retain(|&reg_id| reg_id != KVM_REG_ARM_TIMER_CNT && reg_id != kvm_reg_pc);
 
         let mut regs = Aarch64RegisterVec::default();
         get_registers(&self.fd, &reg_list, &mut regs).map_err(KvmVcpuError::DumpCpuConfig)?;

diff --git a/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_N1_4.14host.json b/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_N1_4.14host.json
@@ -156,10 +156,6 @@
         "addr": "0x603000000010003e",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
       },
-      {
-        "addr": "0x6030000000100040",
-        "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000"
-      },
       {
         "addr": "0x6030000000100042",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001111000101"

diff --git a/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_N1_5.10host.json b/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_N1_5.10host.json
@@ -156,10 +156,6 @@
         "addr": "0x603000000010003e",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
       },
-      {
-        "addr": "0x6030000000100040",
-        "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000"
-      },
       {
         "addr": "0x6030000000100042",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001111000101"

diff --git a/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_N1_6.1host.json b/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_N1_6.1host.json
@@ -156,10 +156,6 @@
         "addr": "0x603000000010003e",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
       },
-      {
-        "addr": "0x6030000000100040",
-        "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000"
-      },
       {
         "addr": "0x6030000000100042",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001111000101"

diff --git a/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_V1_4.14host.json b/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_V1_4.14host.json
@@ -32,10 +32,6 @@
         "addr": "0x6030000000100000",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010001111111000000000000000000000"
       },
-      {
-        "addr": "0x6030000000100002",
-        "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-      },
       {
         "addr": "0x6030000000100004",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"

diff --git a/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_V1_5.10host.json b/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_V1_5.10host.json
@@ -156,10 +156,6 @@
         "addr": "0x603000000010003e",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
       },
-      {
-        "addr": "0x6030000000100040",
-        "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000"
-      },
       {
         "addr": "0x6030000000100042",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001111000101"

diff --git a/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_V1_6.1host.json b/tests/data/cpu_template_helper/fingerprint_ARM_NEOVERSE_V1_6.1host.json
@@ -156,10 +156,6 @@
         "addr": "0x603000000010003e",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
       },
-      {
-        "addr": "0x6030000000100040",
-        "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000"
-      },
       {
         "addr": "0x6030000000100042",
         "bitmap": "0b00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001111000101"