[Qemu-devel] [PATCH v2 3/3] pc: Disable vmdesc submission for old machines

[Alexander Graf]

Older PC machine types might by accident be backwards live migration compatible,
but with the new vmdesc self-describing blob in our live migration stream we
would break that compatibility.

Also users wouldn't expect massive behaviorial differences when updating to a
new version of QEMU while retaining their old machine type, especially not
potential breakage in tooling around live migration.

So disable vmdesc submission for old PC machine types.

Signed-off-by: Alexander Graf <ag...@suse.de>
---
 hw/i386/pc_piix.c | 1 +
 hw/i386/pc_q35.c  | 1 +
 2 files changed, 2 insertions(+)

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 38b42b0..35bc377 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -332,6 +332,7 @@ static void pc_compat_2_2(MachineState *machine)
                                 CPUID_7_0_EBX_HLE | CPUID_7_0_EBX_RTM, 0);
     x86_cpu_compat_set_features("Broadwell", FEAT_7_0_EBX,
                                 CPUID_7_0_EBX_HLE | CPUID_7_0_EBX_RTM, 0);
+    machine->suppress_vmdesc = true;
 }
 
 static void pc_compat_2_1(MachineState *machine)
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 63027ee..1305eb0 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -311,6 +311,7 @@ static void pc_compat_2_2(MachineState *machine)
                                 CPUID_7_0_EBX_HLE | CPUID_7_0_EBX_RTM, 0);
     x86_cpu_compat_set_features("Broadwell", FEAT_7_0_EBX,
                                 CPUID_7_0_EBX_HLE | CPUID_7_0_EBX_RTM, 0);
+    machine->suppress_vmdesc = true;
 }
 
 static void pc_compat_2_1(MachineState *machine)
-- 
1.7.12.4