From: Halil Pasic <pasic@linux.ibm.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Tony Krowiak <akrowiak@linux.ibm.com>,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
cohuck@redhat.com, pasic@linux.vnet.ibm.com,
jjherne@linux.ibm.com, jgg@nvidia.com,
alex.williamson@redhat.com, kwankhede@nvidia.com,
stable@vger.kernel.org, Tony Krowiak <akrowiak@stny.rr.com>
Subject: Re: [PATCH v2] s390/vfio-ap: fix memory leak in mdev remove callback
Date: Wed, 19 May 2021 01:27:09 +0200 [thread overview]
Message-ID: <20210519012709.3bcc30e7.pasic@linux.ibm.com> (raw)
In-Reply-To: <ca5f1c72-09a3-d270-44a0-bda54c554f67@de.ibm.com>
On Tue, 18 May 2021 19:01:42 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> On 18.05.21 17:33, Halil Pasic wrote:
> > On Tue, 18 May 2021 15:59:36 +0200
> > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
[..]
> >>>>
> >>>> Would it help, if the code in priv.c would read the hook once
> >>>> and then only work on the copy? We could protect that with rcu
> >>>> and do a synchronize rcu in vfio_ap_mdev_unset_kvm after
> >>>> unsetting the pointer?
> >
> > Unfortunately just "the hook" is ambiguous in this context. We
> > have kvm->arch.crypto.pqap_hook that is supposed to point to
> > a struct kvm_s390_module_hook member of struct ap_matrix_mdev
> > which is also called pqap_hook. And struct kvm_s390_module_hook
> > has function pointer member named "hook".
>
> I was referring to the full struct.
> >
> >>>
> >>> I'll look into this.
> >>
> >> I think it could work. in priv.c use rcu_readlock, save the
> >> pointer, do the check and call, call rcu_read_unlock.
> >> In vfio_ap use rcu_assign_pointer to set the pointer and
> >> after setting it to zero call sychronize_rcu.
> >
> > In my opinion, we should make the accesses to the
> > kvm->arch.crypto.pqap_hook pointer properly synchronized. I'm
> > not sure if that is what you are proposing. How do we usually
> > do synchronisation on the stuff that lives in kvm->arch?
> >
>
> RCU is a method of synchronization. We make sure that structure
> pqap_hook is still valid as long as we are inside the rcu read
> lock. So the idea is: clear pointer, wait until all old readers
> have finished and the proceed with getting rid of the structure.
Yes I know that RCU is a method of synchronization, but I'm not
very familiar with it. I'm a little confused by "read the hook
once and then work on a copy". I guess, I would have to read up
on the RCU again to get clarity. I intend to brush up my RCU knowledge
once the patch comes along. I would be glad to have your help when
reviewing an RCU based solution for this.
Regards,
Halil
next prev parent reply other threads:[~2021-05-18 23:27 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-10 21:48 [PATCH v2] s390/vfio-ap: fix memory leak in mdev remove callback Tony Krowiak
2021-05-10 21:56 ` Tony Krowiak
2021-05-12 10:35 ` Cornelia Huck
2021-05-12 12:41 ` Jason Gunthorpe
2021-05-12 15:32 ` Christian Borntraeger
2021-05-12 16:50 ` Jason Gunthorpe
2021-05-13 14:19 ` Tony Krowiak
2021-05-13 14:18 ` Tony Krowiak
2021-05-13 17:25 ` Jason Gunthorpe
2021-05-13 17:32 ` Halil Pasic
2021-05-13 17:34 ` Jason Gunthorpe
2021-05-12 16:49 ` Christian Borntraeger
2021-05-12 18:35 ` Halil Pasic
2021-05-13 14:35 ` Tony Krowiak
2021-05-13 17:45 ` Halil Pasic
2021-05-13 19:23 ` Tony Krowiak
2021-05-14 0:15 ` Halil Pasic
2021-05-17 13:37 ` Tony Krowiak
2021-05-17 19:10 ` Halil Pasic
2021-05-18 9:30 ` Christian Borntraeger
2021-05-18 13:42 ` Tony Krowiak
2021-05-18 13:59 ` Christian Borntraeger
2021-05-18 15:33 ` Halil Pasic
2021-05-18 17:01 ` Christian Borntraeger
2021-05-18 23:27 ` Halil Pasic [this message]
2021-05-19 8:17 ` Christian Borntraeger
2021-05-19 11:22 ` Christian Borntraeger
2021-05-19 12:59 ` Halil Pasic
2021-05-19 13:02 ` Jason Gunthorpe
2021-05-19 11:25 ` Halil Pasic
2021-05-18 18:14 ` Tony Krowiak
2021-05-18 18:22 ` Christian Borntraeger
2021-05-18 18:40 ` Tony Krowiak
2021-05-18 13:41 ` Tony Krowiak
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