[PATCH AUTOSEL 4.19 36/49] KVM: PPC: Book3S: Use new mutex to synchronize access to rtas token list

Sasha Levin
2019-06-08T11:45:37Z

From: Paul Mackerras <paulus@ozlabs.org>

[ Upstream commit 1659e27d2bc1ef47b6d031abe01b467f18cb72d9 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/include/asm/kvm_host.h | 1 +
arch/powerpc/kvm/book3s.c | 1 +
arch/powerpc/kvm/book3s_rtas.c | 14 ++++++--------
3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index bccc5051249e..2b6049e83970 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -299,6 +299,7 @@ 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 87348e498c89..281f074581a3 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -840,6 +840,7 @@ 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 2d3b2b1cc272..8f2355138f80 100644
--- 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);
--
2.20.1