Re: [PATCH 4/4] KVM: PPC: Book3S HV: Don't take kvm->lock around kvm_for_each_vcpu

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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,
> 




[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux