linux-kernel - Re: [PATCH] KVM: arm64: Fix circular locking dependency

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Date: Wed, 24 Jan 2024 09:07:33 +0000
From: Sebastian Ene <sebastianene@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
	kernel-team@...roid.com, stable@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fix circular locking dependency

On Tue, Jan 23, 2024 at 05:35:26PM +0000, Oliver Upton wrote:
> On Tue, Jan 23, 2024 at 04:48:19PM +0000, Sebastian Ene wrote:
> > The rule inside kvm enforces that the vcpu->mutex is taken *inside*
> > kvm->lock. The rule is violated by the pkvm_create_hyp_vm which acquires

Hi Oliver,

>                                          ^~~~~~~~~~~~~~~~~~
> 
> nit: always suffix function names with '()'
> 
> > the kvm->lock while already holding the vcpu->mutex lock from
> > kvm_vcpu_ioctl. Follow the rule by taking the config lock while getting the
> > VM handle and make sure that this is cleaned on VM destroy under the
> > same lock.
> 
> It is always better to describe a lock in terms of what data it
> protects, the critical section(s) are rather obvious here.
> 
>   Avoid the circular locking dependency altogether by protecting the hyp
>   vm handle with the config_lock, much like we already do for other
>   forms of VM-scoped data.
> 
> > Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> > Cc: stable@...r.kernel.org
> 
> nitpicks aside, this looks fine.
> 
> Reviewed-by: Oliver Upton <oliver.upton@...ux.dev>
> 

Thanks for the suggestions, I updated the comit message and I will push
a V2 of the patch with the above and the Reviewed-by tag.

Thanks,
Seb

> -- 
> Thanks,
> Oliver