On 5/23/19 8:36 AM, Paul Mackerras wrote:
> 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.
Yes.
Reviewed-by: Cédric Le Goater <clg@xxxxxxxx>
Thanks,
C.
>
> 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,
>
