Some nested qemu VM crashes at grub if launched in dozens

[Luiz Angelo Daros de Luca]

Hello,

I'm using gns3 inside vbox with multiple virtual nodes (openwrt running as qemu vms). If I start all nodes at the same time, some of them crashes during the grub countdown (or a even little bit before) with:

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=00000010 EBX=0000c866 ECX=00040000 EDX=0ff8f7c0
ESI=0ff8f760 EDI=00000005 EBP=00001ff0 ESP=00001ff0
EIP=000082fd EFL=00010006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     00008280 00000027
IDT=     00000000 000003ff
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
EFER=0000000000000000
Code=ef 82 00 00 08 00 66 b8 10 00 8e d8 8e c0 8e e0 8e e8 8e d0 <8b> 04 24 a3 f0 1f 00 00 a1 64 82 00 00 89 c4 89 c5 a1 f0 1f 00 00 89 04 24 31 c0 0f 01 0d

If I restart that nested VM, it should work as expected.

I didn't test 6.1.34 but this bug has been happening at least since 2020.

I also opened an issue with gns3, but it is more likely to be a virtualbox issue: ​https://github.com/GNS3/gns3-gui/issues/3330