[PULL,3/3] microvm: do not use the lastest cpu version

Commit Message

Ani Sinha March 5, 2025, 7:50 a.m. UTC

commit 0788a56bd1ae3 ("i386: Make unversioned CPU models be aliases")
introduced 'default_cpu_version' for PCMachineClass. This created three
categories of CPU models:
 - Most unversioned CPU models would use version 1 by default.
 - For machines 4.0.1 and older that do not support cpu model aliases, a
   special default_cpu_version value of CPU_VERSION_LEGACY is used.
 - It was thought that future machines would use the latest value of cpu
   versions corresponding to default_cpu_version value of
   CPU_VERSION_LATEST [1].

All pc machines still use the default cpu version of 1 for
unversioned cpu models. CPU_VERSION_LATEST is a moving target and
changes with time. Therefore, if machines use CPU_VERSION_LATEST, it would
mean that over a period of time, for the same versioned machine type,
the cpu version would be different depending on what the latest was at that
time. This would break guests even when they use a constant specific
versioned machine type.
Additionally, microvm machines are not versioned anyway and therefore
there is no requirement to use the latest cpu model by default.
Let microvms use the non-versioned cpu model and remove all references
to CPU_VERSION_LATEST as there are no other users (nor we anticipate
future consumers of CPU_VERSION_LATEST).

Those users who need spefific cpu versions can use explicit version in
the QEMU command line to select the specific cpu version desired.

CI pipline does not break with this change.

1) See commit dcafd1ef0af227 ("i386: Register versioned CPU models")

CC: [e-mail]
CC: [e-mail]
Message-ID: <[e-mail]>
Reviewed-by: Igor Mammedov <[e-mail]>
Reviewed-by: Sergio Lopez <[e-mail]>
Signed-off-by: Ani Sinha <[e-mail]>
Reviewed-by: Zhao Liu <[e-mail]>
---
 hw/i386/microvm.c |  2 +-
 target/i386/cpu.c | 15 ---------------
 target/i386/cpu.h |  4 ----
 3 files changed, 1 insertion(+), 20 deletions(-)

Patch

diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c
index d0a236c74f..a340a5fd39 100644
--- a/hw/i386/microvm.c
+++ b/hw/i386/microvm.c
@@ -491,7 +491,7 @@  static void microvm_machine_state_init(MachineState *machine)
 
     microvm_memory_init(mms);
 
-    x86_cpus_init(x86ms, CPU_VERSION_LATEST);
+    x86_cpus_init(x86ms, 1);
 
     microvm_devices_init(mms);
 }
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 0cd9b70938..2da2cf36fd 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5640,18 +5640,6 @@  void x86_cpu_set_default_version(X86CPUVersion version)
     default_cpu_version = version;
 }
 
-static X86CPUVersion x86_cpu_model_last_version(const X86CPUModel *model)
-{
-    int v = 0;
-    const X86CPUVersionDefinition *vdef =
-        x86_cpu_def_get_versions(model->cpudef);
-    while (vdef->version) {
-        v = vdef->version;
-        vdef++;
-    }
-    return v;
-}
-
 /* Return the actual version being used for a specific CPU model */
 static X86CPUVersion x86_cpu_model_resolve_version(const X86CPUModel *model)
 {
@@ -5659,9 +5647,6 @@  static X86CPUVersion x86_cpu_model_resolve_version(const X86CPUModel *model)
     if (v == CPU_VERSION_AUTO) {
         v = default_cpu_version;
     }
-    if (v == CPU_VERSION_LATEST) {
-        return x86_cpu_model_last_version(model);
-    }
     return v;
 }
 
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 10ce019e3f..113cf10aea 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -2740,10 +2740,6 @@  void apic_handle_tpr_access_report(DeviceState *d, target_ulong ip,
                                    TPRAccess access);
 
 /* Special values for X86CPUVersion: */
-
-/* Resolve to latest CPU version */
-#define CPU_VERSION_LATEST -1
-
 /*
  * Resolve to version defined by current machine type.
  * See x86_cpu_set_default_version()