[Bug 65561] KVM:Entry failed on Single stepping sti instruction

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=65561

--- Comment #12 from Paolo Bonzini <bonzini@gnu.org> ---
> Hi, Paolo, thanks for your explanation. I am interested in fixing this. So
> what's the technical challenge here?

The first step is to reproduce the failure.  To do this you can make a 
patch to kvm-unit-tests 
(git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git).

0x80000021 means invalid guest state in the VMCS (the VM information 
that is passed to the processor).  So you could try adding some printk 
to understand what is the invalid guest state.  To do this you need to 
download the Intel manuals (known as "Intel SDM", google is your 
friend).  You can post the testcase patch on kvm@vger.kernel.org once 
you have a reproducer.

> When you say "support for single-stepping and breakpoints in the emulator is
> quite minimal", do you mean it's a problem in the Qemu side, rather than
> something wrong in the kvm kernel modules? If so, and if we want to fix this,
> we need to make some changes in the Qemu code, right?

No, the emulator is part of KVM, see arch/x86/kvm/emulate.c.  I have 
some pending patches for it, destined to 3.17.  There is a small chance 
that they fix the bug.

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