linux-kernel - [PATCH v6 04/33] KVM: x86: Check for existing Hyper-V vCPU in kvm_hv_vcpu

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Date:   Tue, 30 Aug 2022 15:37:08 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v6 04/33] KVM: x86: Check for existing Hyper-V vCPU in kvm_hv_vcpu_init()

From: Sean Christopherson <seanjc@...gle.com>

When potentially allocating/initializing the Hyper-V vCPU struct, check
for an existing instance in kvm_hv_vcpu_init() instead of requiring
callers to perform the check.  Relying on callers to do the check is
risky as it's all too easy for KVM to overwrite vcpu->arch.hyperv and
leak memory, and it adds additional burden on callers without much
benefit.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/hyperv.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 611c349a08bf..8aadd31ed058 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -936,9 +936,12 @@ static void stimer_init(struct kvm_vcpu_hv_stimer *stimer, int timer_index)
 
 static int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
 {
-	struct kvm_vcpu_hv *hv_vcpu;
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
 	int i;
 
+	if (hv_vcpu)
+		return 0;
+
 	hv_vcpu = kzalloc(sizeof(struct kvm_vcpu_hv), GFP_KERNEL_ACCOUNT);
 	if (!hv_vcpu)
 		return -ENOMEM;
@@ -962,11 +965,9 @@ int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages)
 	struct kvm_vcpu_hv_synic *synic;
 	int r;
 
-	if (!to_hv_vcpu(vcpu)) {
-		r = kvm_hv_vcpu_init(vcpu);
-		if (r)
-			return r;
-	}
+	r = kvm_hv_vcpu_init(vcpu);
+	if (r)
+		return r;
 
 	synic = to_hv_synic(vcpu);
 
@@ -1660,10 +1661,8 @@ int kvm_hv_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
 	if (!host && !vcpu->arch.hyperv_enabled)
 		return 1;
 
-	if (!to_hv_vcpu(vcpu)) {
-		if (kvm_hv_vcpu_init(vcpu))
-			return 1;
-	}
+	if (kvm_hv_vcpu_init(vcpu))
+		return 1;
 
 	if (kvm_hv_msr_partition_wide(msr)) {
 		int r;
@@ -1683,10 +1682,8 @@ int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host)
 	if (!host && !vcpu->arch.hyperv_enabled)
 		return 1;
 
-	if (!to_hv_vcpu(vcpu)) {
-		if (kvm_hv_vcpu_init(vcpu))
-			return 1;
-	}
+	if (kvm_hv_vcpu_init(vcpu))
+		return 1;
 
 	if (kvm_hv_msr_partition_wide(msr)) {
 		int r;
@@ -2000,7 +1997,7 @@ void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu)
 		return;
 	}
 
-	if (!to_hv_vcpu(vcpu) && kvm_hv_vcpu_init(vcpu))
+	if (kvm_hv_vcpu_init(vcpu))
 		return;
 
 	hv_vcpu = to_hv_vcpu(vcpu);
-- 
2.37.2