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KVM: PPC: Book3S HV: Don't take kvm->lock around kvm_for_each_vcpu

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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@ozlabs.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras 2019-05-23 16:36:32 +10:00
parent 1659e27d2b
commit 5a3f49364c
1 changed files with 1 additions and 8 deletions
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9
arch/powerpc/kvm/book3s_hv.c
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@ -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,