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From: Oliver Upton <oliver.upton@linux.dev>
To: Jeremy Linton <jeremy.linton@arm.com>
Cc: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kvmarm@lists.linux.dev, Zenghui Yu <yuzenghui@huawei.com>,
	linux-arm-kernel@lists.infradead.org,
	Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH v2 2/4] KVM: arm64: Avoid lock inversion when setting the VM register width
Date: Thu, 23 Mar 2023 20:45:51 +0000	[thread overview]
Message-ID: <ZBy6f1XoO1b4zts1@linux.dev> (raw)
In-Reply-To: <5b355d9f-0191-2631-9745-5ed2d10af0e1@arm.com>

Jeremy,

On Thu, Mar 23, 2023 at 03:09:54PM -0500, Jeremy Linton wrote:
> Hi,
> 
> On 3/16/23 16:14, Oliver Upton wrote:
> > kvm->lock must be taken outside of the vcpu->mutex. Of course, the
> > locking documentation for KVM makes this abundantly clear. Nonetheless,
> > the locking order in KVM/arm64 has been wrong for quite a while; we
> > acquire the kvm->lock while holding the vcpu->mutex all over the shop.
> > 
> > All was seemingly fine until commit 42a90008f890 ("KVM: Ensure lockdep
> > knows about kvm->lock vs. vcpu->mutex ordering rule") caught us with our
> > pants down, leading to lockdep barfing:
> 
> Thanks for looking at this! It had a bit of fuzz applying to -rc3, did I
> miss a required patch?
> 
> This patch makes the lockdep warnings I was seeing go away but I'm seeing
> similar lockdep problem while running the kvm kselftests. In particular I
> think it was "selftests: kvm: debug-exceptions" which threw the warning.

Hmm, that's odd. IIRC the only test that exploded for me w/o the commit
below was arch_timer.

> So, i'm not sure its completely fixed. I ran the previous one a couple weeks
> back before you respun it, and IIRC didn't see any errors.

Thanks for taking this for a spin! This series depends on commit 47053904e182
("KVM: arm64: timers: Convert per-vcpu virtual offset to a global value")
which is only present in kvmarm/fixes at the moment. I had sent out a PR for
this last week but Paolo has yet to pull.

With both Marc's patch and this series I'm unable to reproduce lockdep
warnings w/ selftests or kvmtool. If it isn't too much trouble can you
give kvmarm/fixes plus this series a whirl and see if everything is
addressed?

Otherwise you may have stumbled into some more crud we'll need to
address :)

-- 
Thanks,
Oliver

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  reply	other threads:[~2023-03-23 20:46 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-16 21:14 [PATCH v2 0/4] KVM: arm64: Fix vcpu->mutex v. kvm->lock inversion Oliver Upton
2023-03-16 21:14 ` [PATCH v2 1/4] KVM: arm64: Avoid vcpu->mutex v. kvm->lock inversion in CPU_ON Oliver Upton
2023-03-22 12:02   ` Marc Zyngier
2023-03-23 19:47     ` Oliver Upton
2023-03-16 21:14 ` [PATCH v2 2/4] KVM: arm64: Avoid lock inversion when setting the VM register width Oliver Upton
2023-03-22 12:02   ` Marc Zyngier
2023-03-23 19:20     ` Oliver Upton
2023-03-23 19:43       ` Marc Zyngier
2023-03-23 19:49         ` Oliver Upton
2023-03-23 20:09   ` Jeremy Linton
2023-03-23 20:45     ` Oliver Upton [this message]
2023-03-23 22:45       ` Jeremy Linton
2023-03-16 21:14 ` [PATCH v2 3/4] KVM: arm64: Use config_lock to protect data ordered against KVM_RUN Oliver Upton
2023-03-16 21:14 ` [PATCH v2 4/4] KVM: arm64: Use config_lock to protect vgic state Oliver Upton
2023-03-22 12:02   ` Marc Zyngier
2023-03-23 19:18     ` Oliver Upton
2023-03-23 22:48 ` [PATCH v2 0/4] KVM: arm64: Fix vcpu->mutex v. kvm->lock inversion Jeremy Linton

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