[PATCH AUTOSEL 4.9 15/20] KVM: PPC: Book3S HV: Don't take kvm->lock around kvm_for_each_vcpu

From: Sasha Levin
Date: Sat Jun 08 2019 - 07:54:43 EST

From: Paul Mackerras <paulus@xxxxxxxxxx>

[ Upstream commit 5a3f49364c3ffa1107bd88f8292406e98c5d206c ]

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

Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Reviewed-by: CÃdric Le Goater <clg@xxxxxxxx>
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@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 0a2b247dbc6b..e840f943cd2c 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -374,12 +374,7 @@ 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)
@@ -1098,7 +1093,6 @@ 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);
* If ILE (interrupt little-endian) has changed, update the
@@ -1132,7 +1126,6 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
mask &= 0xFFFFFFFF;
vc->lpcr = (vc->lpcr & ~mask) | (new_lpcr & mask);
- mutex_unlock(&kvm->lock);

static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,