KVM: PPC: Book3S: Use new mutex to synchronize access to rtas token list

Currently the Book 3S KVM code uses kvm->lock to synchronize access
to the kvm->arch.rtas_tokens list.  Because this list is scanned
inside kvmppc_rtas_hcall(), which is called with the vcpu mutex held,
taking kvm->lock cause a lock inversion problem, which could lead to
a deadlock.

To fix this, we add a new mutex, kvm->arch.rtas_token_lock, which nests
inside the vcpu mutexes, and use that instead of kvm->lock when
accessing the rtas token list.

This removes the lockdep_assert_held() in kvmppc_rtas_tokens_free().
At this point we don't hold the new mutex, but that is OK because
kvmppc_rtas_tokens_free() is only called when the whole VM is being
destroyed, and at that point nothing can be looking up a token in
the list.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 26b3ce487ddc5804313ef508cf3f3bec525ac806..d10df677c452a65033aa49e969869ef6aa51639d 100644 (file)
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -309,6 +309,7 @@ struct kvm_arch {
 #ifdef CONFIG_PPC_BOOK3S_64
        struct list_head spapr_tce_tables;
        struct list_head rtas_tokens;
+       struct mutex rtas_token_lock;
        DECLARE_BITMAP(enabled_hcalls, MAX_HCALL_OPCODE/4 + 1);
 #endif
 #ifdef CONFIG_KVM_MPIC

diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index 61a212d0daf023e9c0806f1ef0a101350c2a1a2f..ac5664845acad03fabd9a5a0c3683532c9fae15b 100644 (file)
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -902,6 +902,7 @@ int kvmppc_core_init_vm(struct kvm *kvm)
 #ifdef CONFIG_PPC64
        INIT_LIST_HEAD_RCU(&kvm->arch.spapr_tce_tables);
        INIT_LIST_HEAD(&kvm->arch.rtas_tokens);
+       mutex_init(&kvm->arch.rtas_token_lock);
 #endif
 
        return kvm->arch.kvm_ops->init_vm(kvm);

diff --git a/arch/powerpc/kvm/book3s_rtas.c b/arch/powerpc/kvm/book3s_rtas.c
index 4e178c4c1ea5074d638bbbb3eaa3315f39b2bfe0..b7ae3dfbf00ec0b5ba7f37bd6b153d4ce891362a 100644 (file)
--- a/arch/powerpc/kvm/book3s_rtas.c
+++ b/arch/powerpc/kvm/book3s_rtas.c
@@ -146,7 +146,7 @@ static int rtas_token_undefine(struct kvm *kvm, char *name)
 {
        struct rtas_token_definition *d, *tmp;
 
-       lockdep_assert_held(&kvm->lock);
+       lockdep_assert_held(&kvm->arch.rtas_token_lock);
 
        list_for_each_entry_safe(d, tmp, &kvm->arch.rtas_tokens, list) {
                if (rtas_name_matches(d->handler->name, name)) {
@@ -167,7 +167,7 @@ static int rtas_token_define(struct kvm *kvm, char *name, u64 token)
        bool found;
        int i;
 
-       lockdep_assert_held(&kvm->lock);
+       lockdep_assert_held(&kvm->arch.rtas_token_lock);
 
        list_for_each_entry(d, &kvm->arch.rtas_tokens, list) {
                if (d->token == token)
@@ -206,14 +206,14 @@ int kvm_vm_ioctl_rtas_define_token(struct kvm *kvm, void __user *argp)
        if (copy_from_user(&args, argp, sizeof(args)))
                return -EFAULT;
 
-       mutex_lock(&kvm->lock);
+       mutex_lock(&kvm->arch.rtas_token_lock);
 
        if (args.token)
                rc = rtas_token_define(kvm, args.name, args.token);
        else
                rc = rtas_token_undefine(kvm, args.name);
 
-       mutex_unlock(&kvm->lock);
+       mutex_unlock(&kvm->arch.rtas_token_lock);
 
        return rc;
 }
@@ -245,7 +245,7 @@ int kvmppc_rtas_hcall(struct kvm_vcpu *vcpu)
        orig_rets = args.rets;
        args.rets = &args.args[be32_to_cpu(args.nargs)];
 
-       mutex_lock(&vcpu->kvm->lock);
+       mutex_lock(&vcpu->kvm->arch.rtas_token_lock);
 
        rc = -ENOENT;
        list_for_each_entry(d, &vcpu->kvm->arch.rtas_tokens, list) {
@@ -256,7 +256,7 @@ int kvmppc_rtas_hcall(struct kvm_vcpu *vcpu)
                }
        }
 
-       mutex_unlock(&vcpu->kvm->lock);
+       mutex_unlock(&vcpu->kvm->arch.rtas_token_lock);
 
        if (rc == 0) {
                args.rets = orig_rets;
@@ -282,8 +282,6 @@ void kvmppc_rtas_tokens_free(struct kvm *kvm)
 {
        struct rtas_token_definition *d, *tmp;
 
-       lockdep_assert_held(&kvm->lock);
-
        list_for_each_entry_safe(d, tmp, &kvm->arch.rtas_tokens, list) {
                list_del(&d->list);
                kfree(d);