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From: Marc Zyngier <maz@kernel.org>
To: Reiji Watanabe <reijiw@google.com>
Cc: Oliver Upton <oliver.upton@linux.dev>,
	kvmarm@lists.linux.dev, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ricardo Koller <ricarkol@google.com>,
	Jing Zhang <jingzhangos@google.com>,
	Raghavendra Rao Anata <rananta@google.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH v1 1/2] KVM: arm64: Acquire mp_state_lock in kvm_arch_vcpu_ioctl_vcpu_init()
Date: Wed, 19 Apr 2023 08:12:45 +0100	[thread overview]
Message-ID: <87cz405or6.wl-maz@kernel.org> (raw)
In-Reply-To: <20230419021852.2981107-2-reijiw@google.com>

On Wed, 19 Apr 2023 03:18:51 +0100,
Reiji Watanabe <reijiw@google.com> wrote:
> 
> kvm_arch_vcpu_ioctl_vcpu_init() doesn't acquire mp_state_lock
> when setting the mp_state to KVM_MP_STATE_RUNNABLE. Fix the
> code to acquire the lock.
> 
> Signed-off-by: Reiji Watanabe <reijiw@google.com>
> ---
>  arch/arm64/kvm/arm.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index fbafcbbcc463..388aa4f18f21 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1244,8 +1244,11 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
>  	 */
>  	if (test_bit(KVM_ARM_VCPU_POWER_OFF, vcpu->arch.features))
>  		kvm_arm_vcpu_power_off(vcpu);
> -	else
> +	else {
> +		spin_lock(&vcpu->arch.mp_state_lock);
>  		WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_RUNNABLE);
> +		spin_unlock(&vcpu->arch.mp_state_lock);
> +	}
>  
>  	return 0;
>  }

I'm not entirely convinced that this fixes anything. What does the
lock hazard against given that the write is atomic? But maybe a
slightly more readable of this would be to expand the critical section
this way:

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 4ec888fdd4f7..bb21d0c25de7 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1246,11 +1246,15 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
 	/*
 	 * Handle the "start in power-off" case.
 	 */
+	spin_lock(&vcpu->arch.mp_state_lock);
+
 	if (test_bit(KVM_ARM_VCPU_POWER_OFF, vcpu->arch.features))
-		kvm_arm_vcpu_power_off(vcpu);
+		__kvm_arm_vcpu_power_off(vcpu);
 	else
 		WRITE_ONCE(vcpu->arch.mp_state.mp_state, KVM_MP_STATE_RUNNABLE);
 
+	spin_unlock(&vcpu->arch.mp_state_lock);
+
 	return 0;
 }

Thoughts?

	M.

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

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  reply	other threads:[~2023-04-19  7:14 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-19  2:18 [PATCH v1 0/2] KVM: arm64: Fix bugs related to mp_state updates Reiji Watanabe
2023-04-19  2:18 ` [PATCH v1 1/2] KVM: arm64: Acquire mp_state_lock in kvm_arch_vcpu_ioctl_vcpu_init() Reiji Watanabe
2023-04-19  7:12   ` Marc Zyngier [this message]
2023-04-20  2:13     ` Reiji Watanabe
2023-04-20  8:16       ` Marc Zyngier
2023-04-21  3:27         ` Reiji Watanabe
2023-04-19  2:18 ` [PATCH v1 2/2] KVM: arm64: Have kvm_psci_vcpu_on() use WRITE_ONCE() to update mp_state Reiji Watanabe
2023-04-20  8:08 ` [PATCH v1 0/2] KVM: arm64: Fix bugs related to mp_state updates Marc Zyngier

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