Re: [PATCH v5 5/6] KVM: arm64: use kvm_trylock_all_vcpus when locking all vCPUs

From: Marc Zyngier <maz@kernel.org>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: kvm@vger.kernel.org, Suzuki K Poulose <suzuki.poulose@arm.com>,
	Jing Zhang <jingzhangos@google.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Sebastian Ott <sebott@redhat.com>,
	Shusen Li <lishusen2@huawei.com>,
	Waiman Long <longman@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	Bjorn Helgaas <bhelgaas@google.com>,
	Borislav Petkov <bp@alien8.de>, Anup Patel <anup@brainfault.org>,
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	Alexander Potapenko <glider@google.com>,
	kvmarm@lists.linux.dev,
	Keisuke Nishimura <keisuke.nishimura@inria.fr>,
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	Kunkun Jiang <jiangkunkun@huawei.com>,
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	Randy Dunlap <rdunlap@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>,
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	kvm-riscv@lists.infradead.org, Ingo Molnar <mingo@redhat.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>
Subject: Re: [PATCH v5 5/6] KVM: arm64: use kvm_trylock_all_vcpus when locking all vCPUs
Date: Wed, 14 May 2025 10:35:36 +0100	[thread overview]
Message-ID: <86msbffsbb.wl-maz@kernel.org> (raw)
In-Reply-To: <20250512180407.659015-6-mlevitsk@redhat.com>

On Mon, 12 May 2025 19:04:06 +0100,
Maxim Levitsky <mlevitsk@redhat.com> wrote:
> 
> Use kvm_trylock_all_vcpus instead of a custom implementation when locking
> all vCPUs of a VM, to avoid triggering a lockdep warning, in the case in
> which the VM is configured to have more than MAX_LOCK_DEPTH vCPUs.
> 
> This fixes the following false lockdep warning:
> 
> [  328.171264] BUG: MAX_LOCK_DEPTH too low!
> [  328.175227] turning off the locking correctness validator.
> [  328.180726] Please attach the output of /proc/lock_stat to the bug report
> [  328.187531] depth: 48  max: 48!
> [  328.190678] 48 locks held by qemu-kvm/11664:
> [  328.194957]  #0: ffff800086de5ba0 (&kvm->lock){+.+.}-{3:3}, at: kvm_ioctl_create_device+0x174/0x5b0
> [  328.204048]  #1: ffff0800e78800b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
> [  328.212521]  #2: ffff07ffeee51e98 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
> [  328.220991]  #3: ffff0800dc7d80b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
> [  328.229463]  #4: ffff07ffe0c980b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
> [  328.237934]  #5: ffff0800a3883c78 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
> [  328.246405]  #6: ffff07fffbe480b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
> 
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>

Acked-by: Marc Zyngier <maz@kernel.org>

Paolo: if you are queuing this for 6.16, please put it on a stable
branch so that I can merge it back in case of conflicts.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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