Re: [PATCH 1/6] KVM: nVMX: Get to-be-acknowledge IRQ for nested VM-Exit at injection site

[Sean Christopherson]

On Wed, Sep 04, 2024, Nathan Chancellor wrote:
> I bisected (log below) an issue with starting a nested guest that
> appears on two of my newer Intel test machines (but not a somewhat old
> laptop) when this change as commit 6f373f4d941b ("KVM: nVMX: Get
> to-be-acknowledge IRQ for nested VM-Exit at injection site") in -next is
> present in the host kernel.
> 
> I start a virtual machine with a full distribution using QEMU then start
> a nested virtual machine using QEMU with the same kernel and a much
> simpler Buildroot initrd, just to test the ability to run a nested
> guest. After this change, starting a nested guest results in no output
> from the nested guest and eventually the first guest restarts, sometimes
> printing a lockup message that appears to be caused from qemu-system-x86

*sigh*

It's not you, it's me.

I just bisected hangs in my nested setup to this same commit.  Apparently, I
completely and utterly failed at testing.

There isn't that much going on here, so knock wood, getting a root cause shouldn't
be terribly difficult.