From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-24.mta1.migadu.com (out-24.mta1.migadu.com [95.215.58.24]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AF8A4AD32 for ; Thu, 16 Mar 2023 21:14:31 +0000 (UTC) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1679001269; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LkAwqg0i7yTvKn2mOxOOrm7GaHmSdBwLu5pMrSRUytM=; b=FSd/qQ6pOisIrAv3tCgau7khw7/9tF+lpLR00aeUh1bc6YTa8H4BwCILOztc1x6+TuC5bK pF0jJ1dwqdzVe38DpemCRT2KHlY61fnJkOd6WTNJeD7doFnCgbY1h7vlhhKMG1ptX9HWX/ DOAk5IQo+sywJWacpAmkw1WbxDRAOoM= From: Oliver Upton To: Marc Zyngier Cc: James Morse , Suzuki K Poulose , kvmarm@lists.linux.dev, Zenghui Yu , linux-arm-kernel@lists.infradead.org, Sean Christopherson , Oliver Upton , Jeremy Linton Subject: [PATCH v2 2/4] KVM: arm64: Avoid lock inversion when setting the VM register width Date: Thu, 16 Mar 2023 21:14:10 +0000 Message-Id: <20230316211412.2651555-3-oliver.upton@linux.dev> In-Reply-To: <20230316211412.2651555-1-oliver.upton@linux.dev> References: <20230316211412.2651555-1-oliver.upton@linux.dev> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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: ====================================================== WARNING: possible circular locking dependency detected 6.2.0-rc7+ #19 Not tainted ------------------------------------------------------ qemu-system-aar/859 is trying to acquire lock: ffff5aa69269eba0 (&host_kvm->lock){+.+.}-{3:3}, at: kvm_reset_vcpu+0x34/0x274 but task is already holding lock: ffff5aa68768c0b8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x8c/0xba0 which lock already depends on the new lock. Add a dedicated lock to serialize writes to VM-scoped configuration from the context of a vCPU. Protect the register width flags with the new lock, thus avoiding the need to grab the kvm->lock while holding vcpu->mutex in kvm_reset_vcpu(). Reported-by: Jeremy Linton Link: https://lore.kernel.org/kvmarm/f6452cdd-65ff-34b8-bab0-5c06416da5f6@arm.com/ Signed-off-by: Oliver Upton --- arch/arm64/include/asm/kvm_host.h | 3 +++ arch/arm64/kvm/arm.c | 18 ++++++++++++++++++ arch/arm64/kvm/reset.c | 6 +++--- 3 files changed, 24 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 917586237a4d..1f4b9708a775 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -185,6 +185,9 @@ struct kvm_protected_vm { }; struct kvm_arch { + /* Protects VM-scoped configuration data */ + struct mutex config_lock; + struct kvm_s2_mmu mmu; /* VTCR_EL2 value for this VM */ diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 731a78f85915..1478bec52767 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -128,6 +128,16 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) { int ret; + mutex_init(&kvm->arch.config_lock); + +#ifdef CONFIG_LOCKDEP + /* Clue in lockdep that the config_lock must be taken inside kvm->lock */ + mutex_lock(&kvm->lock); + mutex_lock(&kvm->arch.config_lock); + mutex_unlock(&kvm->arch.config_lock); + mutex_unlock(&kvm->lock); +#endif + ret = kvm_share_hyp(kvm, kvm + 1); if (ret) return ret; @@ -328,6 +338,14 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) spin_lock_init(&vcpu->arch.mp_state_lock); +#ifdef CONFIG_LOCKDEP + /* Inform lockdep that the config_lock is acquired after vcpu->mutex */ + mutex_lock(&vcpu->mutex); + mutex_lock(&vcpu->kvm->arch.config_lock); + mutex_unlock(&vcpu->kvm->arch.config_lock); + mutex_unlock(&vcpu->mutex); +#endif + /* Force users to call KVM_ARM_VCPU_INIT */ vcpu->arch.target = -1; bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES); diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c index b874ec6a37c1..ee445a7a1ef8 100644 --- a/arch/arm64/kvm/reset.c +++ b/arch/arm64/kvm/reset.c @@ -205,7 +205,7 @@ static int kvm_set_vm_width(struct kvm_vcpu *vcpu) is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); - lockdep_assert_held(&kvm->lock); + lockdep_assert_held(&kvm->arch.config_lock); if (test_bit(KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED, &kvm->arch.flags)) { /* @@ -262,9 +262,9 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) bool loaded; u32 pstate; - mutex_lock(&vcpu->kvm->lock); + mutex_lock(&vcpu->kvm->arch.config_lock); ret = kvm_set_vm_width(vcpu); - mutex_unlock(&vcpu->kvm->lock); + mutex_unlock(&vcpu->kvm->arch.config_lock); if (ret) return ret; -- 2.40.0.rc1.284.g88254d51c5-goog