[Qemu-devel] [PATCH] target-i386/machine:fix migrate faile because of Hyper-V HV_X64_MSR_VP_RUNTIME

[Zhuangyanying]

From: ZhuangYanying <address@hidden>

Hyper-V HV_X64_MSR_VP_RUNTIME was introduced in linux-4.4 + qemu-2.5.

As long as the KVM module supports, qemu will save / load the 
vmstate_msr_hyperv_runtime register during the migration.

Regardless of whether the hyperv_runtime configuration of x86_cpu_properties is 
enabled.

The qemu-2.3 does not support this feature, of course, failed to migrate.

linux-BGSfqC:/home/qemu # ./x86_64-softmmu/qemu-system-x86_64 --enable-kvm 
-nodefaults -machine pc-i440fx-2.3,accel=kvm,usb=off -smp 4 -m 4096 -drive 
file=/work/suse/sles11sp3.img.bak,format=raw,if=none,id=drive-virtio-disk0,cache=none
 
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0
 
-vnc :99 -device cirrus-vga,id=video0,vgamem_mb=8,bus=pci.0,addr=0x2 -monitor vc

save_section_header:se->section_id=3,se->idstr:ram,se->instance_id=0,se->version_id=4

save_section_header:se->section_id=0,se->idstr:timer,se->instance_id=0,se->version_id=2

save_section_header:se->section_id=4,se->idstr:cpu_common,se->instance_id=0,se->version_id=1

save_section_header:se->section_id=5,se->idstr:cpu,se->instance_id=0,se->version_id=12

vmstate_subsection_save:vmsd->name:cpu/async_pf_msr

hyperv_runtime_enable_needed:env->msr_hv_runtime=128902811

vmstate_subsection_save:vmsd->name:cpu/msr_hyperv_runtime

Since hyperv_runtime is false, vm will not use hv->runtime_offset, then 
vmstate_msr_hyperv_runtime is no need to transfer while migrating.

Signed-off-by: address@hidden
---
Hi,

Recently, I tested cross-version migration/rollback between qemu tag v2.3.1 and 
qemu-master, found that rollback failed.

linux-rIVrzS:/home/git/qemu # ./x86_64-softmmu/qemu-system-x86_64 --enable-kvm 
-nodefaults -machine pc-i440fx-2.3,accel=kvm,usb=off -smp 4 -m 4096 -drive 
file=/work/suse/sles11sp3.img.bak,format=raw,if=none,id=drive-virtio-disk0,cache=none
 
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0
 
-vnc :99 -device cirrus-vga,id=video0,vgamem_mb=8,bus=pci.0,addr=0x2 -monitor 
vc 
-incoming tcp:0:8888

qemu-system-x86_64: error while loading state for instance 0x0 of device 'cpu'

qemu-system-x86_64: load of migration failed: No such file or directory

Maybe set compat_props on PC_COMPAT_2_5 ? Any better idea?
---
 target-i386/machine.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/target-i386/machine.c b/target-i386/machine.c
index 48037f1..e984d77 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -709,6 +709,10 @@ static bool hyperv_runtime_enable_needed(void *opaque)
     X86CPU *cpu = opaque;
     CPUX86State *env = &cpu->env;
 
+    if (!cpu->hyperv_runtime) {
+        return 0;
+    }
+
     return env->msr_hv_runtime != 0;
 }
 
-- 
1.8.3.1