Re: unhandled vm exit: 0x80000021 vcpu_id 0

[Avi Kivity <avi@redhat.com>]

Gabe Black wrote:
>    Hello again. I'm making more progress getting KVM going in M5, and 
> right now I'm trying to figure out why I'm getting an unhandled vm 
> exit with exit code 0x80000021. According to Intel's manual, something 
> about the guest state isn't being set up correctly. I dumped the 
> initial register state for the 0th virtual CPU and noticed that some 
> things Intel claims are illegal show up there, for instance having 
> paging and protected mode disabled. I'm assuming there's some cooking 
> done to the state as presented to KVM to, for instance, substitute 
> V8086 mode for real mode, etc. I've fixed a number of bugs in M5 that 
> cleaned up some issues, but I'm hoping somebody with more knowledge 
> can tell me what illegal state is still there that would make it 
> through the kvms twiddling and cause VMX to abort. One thing that I 
> know looks funny is that the limit on the IDT is zero, but I haven't 
> been able to find any evidence in the manuals that that's considered 
> wrong rather than just a bad idea. Any help here would be very 
> appreciated!
>

idt.limit = 0 should be fine.

>
> cs 0008 (00000000/ffffffff p 1 dpl 0 db 0 s 1 type a l 1 g 1 avl 0)
> ds 0010 (00000000/ffffffff p 1 dpl 0 db 1 s 1 type 2 l 0 g 1 avl 0)
> es 0010 (00000000/ffffffff p 1 dpl 0 db 1 s 1 type 2 l 0 g 1 avl 0)
> ss 0010 (00000000/ffffffff p 1 dpl 0 db 1 s 1 type 2 l 0 g 1 avl 0)
> fs 0010 (00000000/ffffffff p 1 dpl 0 db 1 s 1 type 2 l 0 g 1 avl 0)
> gs 0010 (00000000/ffffffff p 1 dpl 0 db 1 s 1 type 2 l 0 g 1 avl 0)

Try setting bit 1 (accessed) on the types here.

> tr 0018 (00000000/ffffffff p 1 dpl 0 db 1 s 0 type b l 0 g 1 avl 0)
> ldt 0000 (00000000/00000000 p 0 dpl 0 db 0 s 0 type 0 l 0 g 0 avl 0)
> gdt 76000/17
> idt 0/0
> cr0 80000011 cr2 0 cr3 70000 cr4 20 cr8 0 efer 500

kvm-kmod.git contains a vmx-debug.c which does the same checks as the 
cpu.  If you link it in and call vm_entry_test() just before guest 
entry, it will point out where the state is bad.

-- 
error compiling committee.c: too many arguments to function