[PATCH] kvm: get rid of srcu idx

["Michael S. Tsirkin" <mst@redhat.com>]

srcu_idx is easy to misuse as it can not be used
in nested srcu_read_lock calls.  Switch to local
index to make correctness easier to verify.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---

Lightly tested.

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 311f6da..edb9dfa 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4672,7 +4729,7 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
 	}
 }
 
-static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
+static int vcpu_enter_guest(struct kvm_vcpu *vcpu, int *srcu_idx)
 {
 	int r;
 	bool req_int_win = !irqchip_in_kernel(vcpu->kvm) &&
@@ -4744,7 +4801,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		kvm_lapic_sync_to_vapic(vcpu);
 	}
 
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	srcu_read_unlock(&vcpu->kvm->srcu, *srcu_idx);
 
 	kvm_guest_enter();
 
@@ -4787,7 +4844,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	preempt_enable();
 
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	*srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 
 	/*
 	 * Profile KVM exit RIPs:
@@ -4809,6 +4866,7 @@ out:
 static int __vcpu_run(struct kvm_vcpu *vcpu)
 {
 	int r;
+	int srcu_idx;
 	struct kvm *kvm = vcpu->kvm;
 
 	if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED)) {
@@ -4821,17 +4879,18 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
 	}
 
-	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+	
+	srcu_idx = srcu_read_lock(&kvm->srcu);
 	vapic_enter(vcpu);
 
 	r = 1;
 	while (r > 0) {
 		if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE)
-			r = vcpu_enter_guest(vcpu);
+			r = vcpu_enter_guest(vcpu, &srcu_idx);
 		else {
-			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+			srcu_read_unlock(&kvm->srcu, srcu_idx);
 			kvm_vcpu_block(vcpu);
-			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+			srcu_idx = srcu_read_lock(&kvm->srcu);
 			if (kvm_check_request(KVM_REQ_UNHALT, vcpu))
 			{
 				switch(vcpu->arch.mp_state) {
@@ -4866,13 +4926,13 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 			++vcpu->stat.signal_exits;
 		}
 		if (need_resched()) {
-			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+			srcu_read_unlock(&kvm->srcu, srcu_idx);
 			kvm_resched(vcpu);
-			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+			srcu_idx = srcu_read_lock(&kvm->srcu);
 		}
 	}
 
-	srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
 
 	vapic_exit(vcpu);
 
@@ -4883,6 +4943,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
 	int r;
 	sigset_t sigsaved;
+	int srcu_idx;
 
 	if (vcpu->sigset_active)
 		sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
@@ -4905,9 +4966,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 			vcpu->mmio_read_completed = 1;
 			vcpu->mmio_needed = 0;
 		}
-		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 		r = emulate_instruction(vcpu, 0, 0, EMULTYPE_NO_DECODE);
-		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
 		if (r != EMULATE_DONE) {
 			r = 0;
 			goto out;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c13cc48..60eb9db 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -85,7 +85,6 @@ struct kvm_vcpu {
 	struct kvm_run *run;
 	unsigned long requests;
 	unsigned long guest_debug;
-	int srcu_idx;
 
 	int fpu_active;
 	int guest_fpu_loaded, guest_xcr0_loaded;