arch: Improve arch::Error

Remove unused error enum entries, improve wording and derive
thiserror::Error.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

arch/src/aarch64/mod.rs

@@ -50,7 +50,7 @@ pub enum Error {
 
 impl From<Error> for super::Error {
     fn from(e: Error) -> super::Error {
-        super::Error::AArch64Setup(e)
+        super::Error::PlatformSpecific(e)
     }
 }
 
@@ -185,10 +185,10 @@ pub fn initramfs_load_addr(
             if guest_mem.address_in_range(offset) {
                 Ok(offset.raw_value())
             } else {
-                Err(super::Error::AArch64Setup(Error::InitramfsAddress))
+                Err(super::Error::PlatformSpecific(Error::InitramfsAddress))
             }
         }
-        None => Err(super::Error::AArch64Setup(Error::InitramfsAddress)),
+        None => Err(super::Error::PlatformSpecific(Error::InitramfsAddress)),
     }
 }
 

arch/src/lib.rs

@@ -18,6 +18,7 @@ use std::collections::BTreeMap;
 use std::fmt;
 use std::result;
 use std::sync::Arc;
+use thiserror::Error;
 use versionize::{VersionMap, Versionize, VersionizeError, VersionizeResult};
 use versionize_derive::Versionize;
 use vm_migration::VersionMapped;
@@ -26,31 +27,27 @@ type GuestMemoryMmap = vm_memory::GuestMemoryMmap<vm_memory::bitmap::AtomicBitma
 type GuestRegionMmap = vm_memory::GuestRegionMmap<vm_memory::bitmap::AtomicBitmap>;
 
 /// Type for returning error code.
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum Error {
     #[cfg(target_arch = "x86_64")]
-    /// X86_64 specific error triggered during system configuration.
-    X86_64Setup(x86_64::Error),
+    #[error("Platform specific error (x86_64): {0:?}")]
+    PlatformSpecific(x86_64::Error),
     #[cfg(target_arch = "aarch64")]
-    /// AArch64 specific error triggered during system configuration.
-    AArch64Setup(aarch64::Error),
-    /// The zero page extends past the end of guest_mem.
-    ZeroPagePastRamEnd,
-    /// Error writing the zero page of guest memory.
-    ZeroPageSetup(vm_memory::GuestMemoryError),
-    /// The memory map table extends past the end of guest memory.
+    #[error("Platform specific error (aarch64): {0:?}")]
+    PlatformSpecific(aarch64::Error),
+    #[error("The memory map table extends past the end of guest memory")]
     MemmapTablePastRamEnd,
-    /// Error writing memory map table to guest memory.
+    #[error("Error writing memory map table to guest memory")]
     MemmapTableSetup,
-    /// The hvm_start_info structure extends past the end of guest memory.
+    #[error("The hvm_start_info structure extends past the end of guest memory")]
     StartInfoPastRamEnd,
-    /// Error writing hvm_start_info to guest memory.
+    #[error("Error writing hvm_start_info to guest memory")]
     StartInfoSetup,
-    /// Failed to compute initramfs address.
+    #[error("Failed to compute initramfs address")]
     InitramfsAddress,
-    /// Error writing module entry to guest memory.
-    ModlistSetup(vm_memory::GuestMemoryError),
-    /// RSDP Beyond Guest Memory
+    #[error("Error writing module entry to guest memory: {0}")]
+    ModlistSetup(#[source] vm_memory::GuestMemoryError),
+    #[error("RSDP extends past the end of guest memory")]
     RsdpPastRamEnd,
 }
 

arch/src/x86_64/mod.rs

@@ -197,7 +197,7 @@ pub enum Error {
 
 impl From<Error> for super::Error {
     fn from(e: Error) -> super::Error {
-        super::Error::X86_64Setup(e)
+        super::Error::PlatformSpecific(e)
     }
 }
 

vmm/src/vm.rs

@@ -1180,7 +1180,9 @@ impl Vm {
             self.cpu_manager.lock().unwrap().boot_vcpus() as u64,
         )
         .map_err(|e| {
-            Error::ConfigureSystem(arch::Error::AArch64Setup(arch::aarch64::Error::SetupGic(e)))
+            Error::ConfigureSystem(arch::Error::PlatformSpecific(
+                arch::aarch64::Error::SetupGic(e),
+            ))
         })?;
 
         // PMU interrupt sticks to PPI, so need to be added by 16 to get real irq number.
@@ -1190,7 +1192,9 @@ impl Vm {
             .unwrap()
             .init_pmu(arch::aarch64::fdt::AARCH64_PMU_IRQ + 16)
             .map_err(|_| {
-                Error::ConfigureSystem(arch::Error::AArch64Setup(arch::aarch64::Error::VcpuInitPmu))
+                Error::ConfigureSystem(arch::Error::PlatformSpecific(
+                    arch::aarch64::Error::VcpuInitPmu,
+                ))
             })?;
 
         arch::configure_system(