refactor(cpu-template-helper): Exclude meaningless registers for aarch64

As done for x86, limits `dump_cpu_config()`'s output to the dumpable
registers instead excludes dumpable but not meaningful registers on the
CPU template helper tool's side.

Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

src/cpu-template-helper/src/template/dump/aarch64.rs

@@ -1,7 +1,7 @@
 // Copyright 2023 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-use vmm::arch::aarch64::regs::RegSize;
+use vmm::arch::aarch64::regs::{RegSize, PC, SYS_CNTPCT_EL0, SYS_CNTV_CVAL_EL0};
 use vmm::cpu_config::aarch64::custom_cpu_template::RegisterModifier;
 use vmm::cpu_config::templates::{CpuConfiguration, CustomCpuTemplate, RegisterValueFilter};
 use vmm::logger::warn;
@@ -26,6 +26,9 @@ pub fn config_to_template(cpu_config: &CpuConfiguration) -> CustomCpuTemplate {
             }
         })
         .collect();
+
+    reg_modifiers.retain(|modifier| !REG_EXCLUSION_LIST.contains(&modifier.addr));
+
     reg_modifiers.sort_by_key(|modifier| modifier.addr);
 
     CustomCpuTemplate {
@@ -34,9 +37,20 @@ pub fn config_to_template(cpu_config: &CpuConfiguration) -> CustomCpuTemplate {
     }
 }
 
+// List of register IDs excluded from the CPU configuration dump.
+const REG_EXCLUSION_LIST: [u64; 3] = [
+    // SYS_CNTV_CVAL_EL0 and SYS_CNTPCT_EL0 are timer registers and depend on the elapsed time.
+    // This type of registers are not useful as guest CPU config dump.
+    SYS_CNTV_CVAL_EL0,
+    SYS_CNTPCT_EL0,
+    // Program counter (PC) value 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.
+    PC,
+];
+
 #[cfg(test)]
 mod tests {
-    use vmm::arch::aarch64::regs::{Aarch64RegisterRef, Aarch64RegisterVec};
+    use vmm::arch::aarch64::regs::{reg_size, Aarch64RegisterRef, Aarch64RegisterVec};
 
     use super::*;
 
@@ -64,10 +78,16 @@ mod tests {
             KVM_REG_SIZE_U64,
             &0x0000_ffff_0000_ffff_u64.to_le_bytes(),
         ));
+        // CPU templates only supports 32, 64 and 128 bit wide registers, so the following registers
+        // should be excluded from the result.
         v.push(Aarch64RegisterRef::new(KVM_REG_SIZE_U256, &[0x69; 32]));
         v.push(Aarch64RegisterRef::new(KVM_REG_SIZE_U512, &[0x69; 64]));
         v.push(Aarch64RegisterRef::new(KVM_REG_SIZE_U1024, &[0x69; 128]));
         v.push(Aarch64RegisterRef::new(KVM_REG_SIZE_U2048, &[0x69; 256]));
+        // The following registers should be excluded from the result.
+        for id in REG_EXCLUSION_LIST {
+            v.push(Aarch64RegisterRef::new(id, &vec![0; reg_size(id)]));
+        }
         v
     }
 

src/vmm/src/vstate/vcpu/aarch64.rs

@@ -10,9 +10,7 @@ use std::fmt::{Debug, Write};
 use kvm_ioctls::*;
 use serde::{Deserialize, Serialize};
 
-use crate::arch::aarch64::regs::{
-    Aarch64RegisterVec, KVM_REG_ARM64_SVE_VLS, PC, SYS_CNTPCT_EL0, SYS_CNTV_CVAL_EL0,
-};
+use crate::arch::aarch64::regs::{Aarch64RegisterVec, KVM_REG_ARM64_SVE_VLS};
 use crate::arch::aarch64::vcpu::{
     get_all_registers, get_all_registers_ids, get_mpidr, get_mpstate, get_registers, set_mpstate,
     set_register, setup_boot_regs, VcpuError as ArchError,
@@ -220,17 +218,7 @@ impl KvmVcpu {
 
     /// Dumps CPU configuration.
     pub fn dump_cpu_config(&self) -> Result<CpuConfiguration, KvmVcpuError> {
-        let mut reg_list = get_all_registers_ids(&self.fd).map_err(KvmVcpuError::DumpCpuConfig)?;
-
-        // SYS_CNTV_CVAL_EL0 and SYS_CNTPCT_EL0 are timer registers and depend on the elapsed time.
-        // This type of registers are not useful as guest CPU config dump.
-        //
-        // 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 != SYS_CNTV_CVAL_EL0 && reg_id != SYS_CNTPCT_EL0 && reg_id != PC
-        });
+        let reg_list = get_all_registers_ids(&self.fd).map_err(KvmVcpuError::DumpCpuConfig)?;
 
         let mut regs = Aarch64RegisterVec::default();
         get_registers(&self.fd, &reg_list, &mut regs).map_err(KvmVcpuError::DumpCpuConfig)?;