On 07/06/2017 03:01 PM, Paolo Bonzini wrote:
>
>
> On 06/07/2017 14:51, Christian Borntraeger wrote:
>> We do use rcu to protect the pid pointer. Mark it as such and
>> adopt all code to use the proper access methods.
>>
>> This was detected by sparse.
>> "virt/kvm/kvm_main.c:2248:15: error: incompatible types in comparison
>> expression (different address spaces)"
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>> ---
>> include/linux/kvm_host.h | 2 +-
>> virt/kvm/kvm_main.c | 15 +++++++++++----
>> 2 files changed, 12 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 0b50e7b..bcd37b8 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -234,7 +234,7 @@ struct kvm_vcpu {
>>
>> int guest_fpu_loaded, guest_xcr0_loaded;
>> struct swait_queue_head wq;
>> - struct pid *pid;
>> + struct pid __rcu *pid;
>> int sigset_active;
>> sigset_t sigset;
>> struct kvm_vcpu_stat stat;
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index 19f0ecb..7bd5509 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -293,7 +293,12 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_init);
>>
>> void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
>> {
>> - put_pid(vcpu->pid);
>> + /*
>> + * no need for rcu_read_lock as VCPU_RUN is the only place that
>> + * will change the vcpu->pid pointer and on uninit all file
>> + * descriptors are already gone.
>> + */
>> + put_pid(rcu_dereference(vcpu->pid));
>> kvm_arch_vcpu_uninit(vcpu);
>> free_page((unsigned long)vcpu->run);
>> }
>> @@ -2551,13 +2556,14 @@ static long kvm_vcpu_ioctl(struct file *filp,
>> if (r)
>> return r;
>> switch (ioctl) {
>> - case KVM_RUN:
>> + case KVM_RUN: {
>> + struct pid *oldpid;
>> r = -EINVAL;
>> if (arg)
>> goto out;
>> - if (unlikely(vcpu->pid != current->pids[PIDTYPE_PID].pid)) {
>> + oldpid = rcu_dereference(vcpu->pid);
>> + if (unlikely(oldpid != current->pids[PIDTYPE_PID].pid)) {
>
> Since we never dereference oldpid, the rcu_dereference should be
> rcu_access_pointer instead.
Right. Will fix and send a v2.
>
> Otherwise
>
> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
>> /* The thread running this VCPU changed. */
>> - struct pid *oldpid = vcpu->pid;
>> struct pid *newpid = get_task_pid(current, PIDTYPE_PID);
>>
>> rcu_assign_pointer(vcpu->pid, newpid);
>> @@ -2568,6 +2574,7 @@ static long kvm_vcpu_ioctl(struct file *filp,
>> r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
>> trace_kvm_userspace_exit(vcpu->run->exit_reason, r);
>> break;
>> + }
>> case KVM_GET_REGS: {
>> struct kvm_regs *kvm_regs;
>>
>>
>
