[Qemu-devel] An emulation failure occurs, if I hotplug vcpus immediately after the VM start

[xuyandong]

Hi there,

I am doing some test on qemu vcpu hotplug and I run into some trouble.
An emulation failure occurs and qemu prints the following msg:

KVM internal error. Suberror: 1
emulation failure
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000600
ESI=00000000 EDI=00000000 EBP=00000000 ESP=0000fff8
EIP=0000ff53 EFL=00010082 [--S----] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0000 00000000 0000ffff 00009300
CS =f000 000f0000 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 00008b00if
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=31 d2 eb 04 66 83 ca ff 66 89 d0 66 5b 66 c3 66 89 d0 66 c3 <cf> 66 68 21 
8a 00 00 e9 08 d7 66 56 66 53 66 83 ec 0c 66 89 c3 66 e8 ce 7b ff ff 66 89 c6

I notice that guest is still running SeabBIOS in real mode when the vcpu has 
just been pluged.
This emulation failure can be steadly reproduced if I am doing vcpu hotplug 
during VM launch process.
After some digging, I find this KVM internal error shows up because KVM cannot 
emulate some MMIO (gpa 0xfff53 ).

So I am confused,
(1) does qemu support vcpu hotplug even if guest is running seabios ?
(2) the gpa (0xfff53) is an address of BIOS ROM section, why does kvm confirm 
it as a mmio address incorrectly?