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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* linzhecheng (linzhecheng@huawei.com) wrote:
> 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:

Remember that migrating using -cpu host  across different CPU models is NOT
expected to work.

> 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?

It would seem good if we can make the migration fail there rather than
hitting that KVM error.
It looks like we need to do a bit of plumbing to convert the places that
call it to return a bool rather than void.

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK