[PATCH 2/3] powerpc/kvm: fix rare but potential deadlock scene

[Liu ping fan]

On Wed, Nov 6, 2013 at 1:04 PM, Paul Mackerras <paulus at samba.org> wrote:
> On Tue, Nov 05, 2013 at 03:42:43PM +0800, Liu Ping Fan wrote:
>> Since kvmppc_hv_find_lock_hpte() is called from both virtmode and
>> realmode, so it can trigger the deadlock.
>
> Good catch, we should have preemption disabled while ever we have a
> HPTE locked.
>
>> @@ -474,8 +474,10 @@ static int kvmppc_mmu_book3s_64_hv_xlate(struct kvm_vcpu *vcpu, gva_t eaddr,
>>       }
>>
>>       /* Find the HPTE in the hash table */
>> +     preempt_disable();
>>       index = kvmppc_hv_find_lock_hpte(kvm, eaddr, slb_v,
>>                                        HPTE_V_VALID | HPTE_V_ABSENT);
>> +     preempt_enable();
>
> Which means we need to add the preempt_enable after unlocking the
> HPTE, not here.
>
Yes. Sorry, but I am not sure about whether we can call
preempt_disable/enable() in realmode. I think since thread_info is
allocated with linear address, so we can use preempt_disable/enable()
inside kvmppc_hv_find_lock_hpte(), right?

Thanks and regards,
Pingfan

> Regards,
> Paul.