[Qemu-devel] [Bug Report] vm paused after succeeding to migrate

[linzhecheng]

Hi, all
I encounterd a bug when I try to migrate a windows vm.

Enviroment information:
host A: cpu E5620(model WestmereEP without flag xsave)
host B: cpu E5-2643(model SandyBridgeEP with xsave)

The reproduce steps is :
1. Start a windows 2008 vm with -cpu host(which means host-passthrough).
2. Migrate the vm to host B when cr4.OSXSAVE=0 (successfully).
3. Vm runs on host B for a while so that cr4.OSXSAVE changes to 1.
4. Then migrate the vm to host A (successfully), but vm was paused, and qemu 
printed log as followed:

KVM: entry failed, hardware error 0x80000021

If you're running a guest on an Intel machine without unrestricted mode
support, the failure can be most likely due to the guest entering an invalid
state for Intel VT. For example, the guest maybe running in big real mode
which is not supported on less recent Intel processors.

EAX=019b3bb0 EBX=01a3ae80 ECX=01a61ce8 EDX=00000000
ESI=01a62000 EDI=00000000 EBP=00000000 ESP=01718b20
EIP=0185d982 EFL=00000286 [--S--P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0000 00000000 0000ffff 00009300
CS =f000 ffff0000 0000ffff 00009b00
SS =0000 00000000 0000ffff 00009300
DS =0000 00000000 0000ffff 00009300
FS =0000 00000000 0000ffff 00009300
GS =0000 00000000 0000ffff 00009300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 0000ffff
IDT=     00000000 0000ffff
CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 
DR3=0000000000000000
DR6=00000000ffff0ff0 DR7=0000000000000400
EFER=0000000000000000
Code=00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

I have found that problem happened when kvm_put_sregs returns err -22(called by 
kvm_arch_put_registers(qemu)).
Because kvm_arch_vcpu_ioctl_set_sregs(kvm-mod) checked that guest_cpuid_has no 
X86_FEATURE_XSAVE but cr4.OSXSAVE=1.
So should we cancel migration when kvm_arch_put_registers returns error?