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From: Alexandru Elisei <alexandru.elisei@arm.com>
To: linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, maz@kernel.org,
	james.morse@arm.com, julien.thierry.kdev@gmail.com,
	suzuki.poulose@arm.com
Subject: [PATCH 3/5] KVM: arm64: Move double-checked lock to kvm_vgic_map_resources()
Date: Tue,  1 Dec 2020 15:01:55 +0000	[thread overview]
Message-ID: <20201201150157.223625-4-alexandru.elisei@arm.com> (raw)
In-Reply-To: <20201201150157.223625-1-alexandru.elisei@arm.com>

kvm_vgic_map_resources() is called when a VCPU if first run and it maps all
the VGIC MMIO regions. To prevent double-initialization, the VGIC uses the
ready variable to keep track of the state of resources and the global KVM
mutex to protect against concurrent accesses. After the lock is taken, the
variable is checked again in case another VCPU took the lock between the
current VCPU reading ready equals false and taking the lock.

The double-checked lock pattern is spread across four different functions:
in kvm_vcpu_first_run_init(), in kvm_vgic_map_resource() and in
vgic_{v2,v3}_map_resources(), which makes it hard to reason about and
introduces minor code duplication. Consolidate the checks in
kvm_vgic_map_resources(), where the lock is taken.

No functional change intended.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arch/arm64/kvm/arm.c            | 8 +++-----
 arch/arm64/kvm/vgic/vgic-init.c | 6 ++++++
 arch/arm64/kvm/vgic/vgic-v2.c   | 3 ---
 arch/arm64/kvm/vgic/vgic-v3.c   | 3 ---
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 9d69d2bf6943..65a5e89f5133 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -530,11 +530,9 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
 		 * Map the VGIC hardware resources before running a vcpu the
 		 * first time on this VM.
 		 */
-		if (unlikely(!vgic_ready(kvm))) {
-			ret = kvm_vgic_map_resources(kvm);
-			if (ret)
-				return ret;
-		}
+		ret = kvm_vgic_map_resources(kvm);
+		if (ret)
+			return ret;
 	} else {
 		/*
 		 * Tell the rest of the code that there are userspace irqchip
diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 32e32d67a127..a2f4d1c85f00 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -428,7 +428,13 @@ int kvm_vgic_map_resources(struct kvm *kvm)
 	struct vgic_dist *dist = &kvm->arch.vgic;
 	int ret = 0;
 
+	if (likely(vgic_ready(kvm)))
+		return 0;
+
 	mutex_lock(&kvm->lock);
+	if (vgic_ready(kvm))
+		goto out;
+
 	if (!irqchip_in_kernel(kvm))
 		goto out;
 
diff --git a/arch/arm64/kvm/vgic/vgic-v2.c b/arch/arm64/kvm/vgic/vgic-v2.c
index ebf53a4e1296..7f38c1a93639 100644
--- a/arch/arm64/kvm/vgic/vgic-v2.c
+++ b/arch/arm64/kvm/vgic/vgic-v2.c
@@ -306,9 +306,6 @@ int vgic_v2_map_resources(struct kvm *kvm)
 	struct vgic_dist *dist = &kvm->arch.vgic;
 	int ret = 0;
 
-	if (vgic_ready(kvm))
-		goto out;
-
 	if (IS_VGIC_ADDR_UNDEF(dist->vgic_dist_base) ||
 	    IS_VGIC_ADDR_UNDEF(dist->vgic_cpu_base)) {
 		kvm_err("Need to set vgic cpu and dist addresses first\n");
diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index 9cdf39a94a63..35029c5cb0f1 100644
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -500,9 +500,6 @@ int vgic_v3_map_resources(struct kvm *kvm)
 	int ret = 0;
 	int c;
 
-	if (vgic_ready(kvm))
-		goto out;
-
 	kvm_for_each_vcpu(c, vcpu, kvm) {
 		struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
 
-- 
2.29.2

_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, maz@kernel.org,
	james.morse@arm.com, julien.thierry.kdev@gmail.com,
	suzuki.poulose@arm.com
Subject: [PATCH 3/5] KVM: arm64: Move double-checked lock to kvm_vgic_map_resources()
Date: Tue,  1 Dec 2020 15:01:55 +0000	[thread overview]
Message-ID: <20201201150157.223625-4-alexandru.elisei@arm.com> (raw)
In-Reply-To: <20201201150157.223625-1-alexandru.elisei@arm.com>

kvm_vgic_map_resources() is called when a VCPU if first run and it maps all
the VGIC MMIO regions. To prevent double-initialization, the VGIC uses the
ready variable to keep track of the state of resources and the global KVM
mutex to protect against concurrent accesses. After the lock is taken, the
variable is checked again in case another VCPU took the lock between the
current VCPU reading ready equals false and taking the lock.

The double-checked lock pattern is spread across four different functions:
in kvm_vcpu_first_run_init(), in kvm_vgic_map_resource() and in
vgic_{v2,v3}_map_resources(), which makes it hard to reason about and
introduces minor code duplication. Consolidate the checks in
kvm_vgic_map_resources(), where the lock is taken.

No functional change intended.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arch/arm64/kvm/arm.c            | 8 +++-----
 arch/arm64/kvm/vgic/vgic-init.c | 6 ++++++
 arch/arm64/kvm/vgic/vgic-v2.c   | 3 ---
 arch/arm64/kvm/vgic/vgic-v3.c   | 3 ---
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 9d69d2bf6943..65a5e89f5133 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -530,11 +530,9 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
 		 * Map the VGIC hardware resources before running a vcpu the
 		 * first time on this VM.
 		 */
-		if (unlikely(!vgic_ready(kvm))) {
-			ret = kvm_vgic_map_resources(kvm);
-			if (ret)
-				return ret;
-		}
+		ret = kvm_vgic_map_resources(kvm);
+		if (ret)
+			return ret;
 	} else {
 		/*
 		 * Tell the rest of the code that there are userspace irqchip
diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 32e32d67a127..a2f4d1c85f00 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -428,7 +428,13 @@ int kvm_vgic_map_resources(struct kvm *kvm)
 	struct vgic_dist *dist = &kvm->arch.vgic;
 	int ret = 0;
 
+	if (likely(vgic_ready(kvm)))
+		return 0;
+
 	mutex_lock(&kvm->lock);
+	if (vgic_ready(kvm))
+		goto out;
+
 	if (!irqchip_in_kernel(kvm))
 		goto out;
 
diff --git a/arch/arm64/kvm/vgic/vgic-v2.c b/arch/arm64/kvm/vgic/vgic-v2.c
index ebf53a4e1296..7f38c1a93639 100644
--- a/arch/arm64/kvm/vgic/vgic-v2.c
+++ b/arch/arm64/kvm/vgic/vgic-v2.c
@@ -306,9 +306,6 @@ int vgic_v2_map_resources(struct kvm *kvm)
 	struct vgic_dist *dist = &kvm->arch.vgic;
 	int ret = 0;
 
-	if (vgic_ready(kvm))
-		goto out;
-
 	if (IS_VGIC_ADDR_UNDEF(dist->vgic_dist_base) ||
 	    IS_VGIC_ADDR_UNDEF(dist->vgic_cpu_base)) {
 		kvm_err("Need to set vgic cpu and dist addresses first\n");
diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index 9cdf39a94a63..35029c5cb0f1 100644
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -500,9 +500,6 @@ int vgic_v3_map_resources(struct kvm *kvm)
 	int ret = 0;
 	int c;
 
-	if (vgic_ready(kvm))
-		goto out;
-
 	kvm_for_each_vcpu(c, vcpu, kvm) {
 		struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
 
-- 
2.29.2


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2020-12-01 15:00 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-01 15:01 [PATCH 0/5] KVM: arm64: Miscellaneous improvements Alexandru Elisei
2020-12-01 15:01 ` Alexandru Elisei
2020-12-01 15:01 ` [PATCH 1/5] KVM: Documentation: Add arm64 KVM_RUN error codes Alexandru Elisei
2020-12-01 15:01   ` Alexandru Elisei
2020-12-01 15:01 ` [PATCH 2/5] KVM: arm64: arch_timer: Remove VGIC initialization check Alexandru Elisei
2020-12-01 15:01   ` Alexandru Elisei
2020-12-14 12:45   ` Auger Eric
2020-12-14 12:45     ` Auger Eric
2020-12-01 15:01 ` Alexandru Elisei [this message]
2020-12-01 15:01   ` [PATCH 3/5] KVM: arm64: Move double-checked lock to kvm_vgic_map_resources() Alexandru Elisei
2020-12-14 12:55   ` Auger Eric
2020-12-14 12:55     ` Auger Eric
2020-12-27 14:36     ` Marc Zyngier
2020-12-27 14:36       ` Marc Zyngier
2020-12-01 15:01 ` [PATCH 4/5] KVM: arm64: Update comment in kvm_vgic_map_resources() Alexandru Elisei
2020-12-01 15:01   ` Alexandru Elisei
2020-12-14 12:59   ` Auger Eric
2020-12-14 12:59     ` Auger Eric
2020-12-01 15:01 ` [PATCH 5/5] KVM: arm64: Remove redundant call to kvm_pmu_vcpu_reset() Alexandru Elisei
2020-12-01 15:01   ` Alexandru Elisei
2020-12-14 13:48   ` Auger Eric
2020-12-14 13:48     ` Auger Eric
2020-12-14 14:02     ` Alexandru Elisei
2020-12-14 14:02       ` Alexandru Elisei
2020-12-15  9:15       ` Auger Eric
2020-12-15  9:15         ` Auger Eric
2020-12-27 14:41 ` [PATCH 0/5] KVM: arm64: Miscellaneous improvements Marc Zyngier
2020-12-27 14:41   ` Marc Zyngier

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