linux-kernel - Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated devices

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: <5819E358.4080706@intel.com>
Date:   Wed, 02 Nov 2016 21:00:08 +0800
From:   Jike Song <jike.song@...el.com>
To:     Kirti Wankhede <kwankhede@...dia.com>
CC:     Alexey Kardashevskiy <aik@...abs.ru>, alex.williamson@...hat.com,
        pbonzini@...hat.com, kraxel@...hat.com, cjia@...dia.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        kevin.tian@...el.com, qemu-devel@...gnu.org,
        bjsdjshi@...ux.vnet.ibm.com
Subject: Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated
 devices

On 11/02/2016 08:41 PM, Kirti Wankhede wrote:
> On 11/2/2016 5:51 PM, Jike Song wrote:
>> On 11/02/2016 12:09 PM, Alexey Kardashevskiy wrote:
>>> Or you could just reference and use @mm as KVM and others do. Or there is
>>> anything else you need from @current than just @mm?
>>>
>>
>> I agree. If @mm is the only thing needed, there is really no reason to
>> refer to the @task :-)
>>
> 
> In vfio_lock_acct(), that is for page accounting, if mm->mmap_sem is
> already held then page accounting is deferred, where task structure is
> used to get mm and work is deferred only if mm exist:
> 	mm = get_task_mm(task);
> 
> That is where this module need task structure.

Kirti,

By calling get_task_mm you hold a ref on @mm and save it in iommu,
whenever you want to do something like vfio_lock_acct(), use that mm
(as you said, if mmap_sem not accessible then defer it to a work, but
still @mm is the whole information), and put it after the usage.

I still can't see any reason that the @task have to be saved. It's
always the @mm all the time. Did I miss anything?

--
Thanks,
Jike