linux-kernel - Re: [PATCH] KVM: arm64: Mark the VM as dead for failed initializations

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Message-ID: <Zx_GDqLO4lBQHnxL@linux.dev>
Date: Mon, 28 Oct 2024 10:12:46 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: Raghavendra Rao Ananta <rananta@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, stable@...r.kernel.org,
	syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH] KVM: arm64: Mark the VM as dead for failed
 initializations

On Mon, Oct 28, 2024 at 09:43:45AM -0700, Raghavendra Rao Ananta wrote:
> On Sat, Oct 26, 2024 at 7:53 AM Oliver Upton <oliver.upton@...ux.dev> wrote:
> > On Sat, Oct 26, 2024 at 08:43:21AM +0100, Marc Zyngier wrote:
> > > I think this would fix the problem you're seeing without changing the
> > > userspace view of an erroneous configuration. It would also pave the
> > > way for the complete removal of the interrupt notification to
> > > userspace, which I claim has no user and is just a shit idea.
> >
> > Yeah, looks like this ought to get it done.
> >
> > Even with a fix for this particular issue I do wonder if we should
> > categorically harden against late initialization failures and un-init
> > the vCPU (or bug VM, where necessary) to avoid dealing with half-baked
> > vCPUs/VMs across our UAPI surfaces.
> >
> > A sane userspace will probably crash when KVM_RUN returns EINVAL anyway.
> 
> Thanks for the suggestion. Sure, I'll take another look at the
> possible things that we can uninitialize and try to re-spin the patch.
> 
> Marc,
> 
> If you feel userspace_irqchip_in_use is not necessary anymore, and as
> a quick fix to this issue, we can get rid of that independent of the
> un-init effort.

It's a good cleanup to begin with, even better that it fixes a genuine
bug.

Raghu, could you please test Marc's diff and send it as a patch (w/
correct attribution) if it works? I'm willing to bet that we have more
init/uninit bugs lurking, so we can still follow up w/ robustness
improvements once we're happy w/ the shape of them.

-- 
Thanks,
Oliver