Currently the HV KVM code takes the kvm->lock around calls to
kvm_for_each_vcpu() and kvm_get_vcpu_by_id() (which can call
kvm_for_each_vcpu() internally). However, that leads to a lock
order inversion problem, because these are called in contexts where
the vcpu mutex is held, but the vcpu mutexes nest within kvm->lock
according to Documentation/virtual/kvm/locking.txt. Hence there
is a possibility of deadlock.
To fix this, we simply don't take the kvm->lock mutex around these
calls. This is safe because the implementations of kvm_for_each_vcpu()
and kvm_get_vcpu_by_id() have been designed to be able to be called
locklessly.
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index b1c0a9b..27054d3 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -446,12 +446,7 @@ static void kvmppc_dump_regs(struct kvm_vcpu *vcpu)
static struct kvm_vcpu *kvmppc_find_vcpu(struct kvm *kvm, int id)
{
- struct kvm_vcpu *ret;
-
- mutex_lock(&kvm->lock);
- ret = kvm_get_vcpu_by_id(kvm, id);
- mutex_unlock(&kvm->lock);
- return ret;
+ return kvm_get_vcpu_by_id(kvm, id);
}
static void init_vpa(struct kvm_vcpu *vcpu, struct lppaca *vpa)
@@ -1583,7 +1578,6 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
struct kvmppc_vcore *vc = vcpu->arch.vcore;
u64 mask;
- mutex_lock(&kvm->lock);
spin_lock(&vc->lock);
/*
* If ILE (interrupt little-endian) has changed, update the
@@ -1623,7 +1617,6 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
mask &= 0xFFFFFFFF;
vc->lpcr = (vc->lpcr & ~mask) | (new_lpcr & mask);
spin_unlock(&vc->lock);
- mutex_unlock(&kvm->lock);
}
static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
--
2.7.4
