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

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Message-ID: <Ztjj8xrWMzzrlbtM@google.com>
Date: Wed, 4 Sep 2024 15:49:23 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chao Gao <chao.gao@...el.com>, Zeng Guang <guang.zeng@...el.com>
Subject: Re: [PATCH 1/6] KVM: nVMX: Get to-be-acknowledge IRQ for nested
 VM-Exit at injection site

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.