linux-kernel - Re: [PATCH v2 4/9] iommu/ioasid: Add reference couting functions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200825102048.GB3252704@myrica>
Date:   Tue, 25 Aug 2020 12:20:48 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Jacob Pan <jacob.pan.linux@...il.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>, Wu Hao <hao.wu@...el.com>
Subject: Re: [PATCH v2 4/9] iommu/ioasid: Add reference couting functions

On Mon, Aug 24, 2020 at 10:26:55AM +0800, Lu Baolu wrote:
> Hi Jacob,
> 
> On 8/22/20 12:35 PM, Jacob Pan wrote:
> > There can be multiple users of an IOASID, each user could have hardware
> > contexts associated with the IOASID. In order to align lifecycles,
> > reference counting is introduced in this patch. It is expected that when
> > an IOASID is being freed, each user will drop a reference only after its
> > context is cleared.
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
[...]
> > +/**
> >    * ioasid_find - Find IOASID data
> >    * @set: the IOASID set
> >    * @ioasid: the IOASID to find
> 
> Do you need to increase the refcount of the found ioasid and ask the
> caller to drop it after use? Otherwise, the ioasid might be freed
> elsewhere.

ioasid_find() takes a getter function as parameter, which ensures that the
returned data is valid. It fetches the IOASID data under rcu_read_lock()
and calls the getter on the private data (for example mmget_not_zero() for
bare-metal SVA). Given that, I don't think returning with a reference to
the IOASID is necessary. The IOASID may be freed once ioasid_find()
returns but not the returned data.

Thanks,
Jean