[PATCH] kvm: get rid of srcu idx

[Michael S. Tsirkin]

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 <m...@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;
--
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