From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Kirti Wankhede <kwankhede@nvidia.com>, Jike Song <jike.song@intel.com>
Cc: alex.williamson@redhat.com, pbonzini@redhat.com,
kraxel@redhat.com, cjia@nvidia.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, kevin.tian@intel.com,
qemu-devel@nongnu.org, bjsdjshi@linux.vnet.ibm.com
Subject: Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated devices
Date: Thu, 3 Nov 2016 15:29:54 +1100 [thread overview]
Message-ID: <dbad95e6-e6ba-3da0-34bc-9981e0d633f7@ozlabs.ru> (raw)
In-Reply-To: <4918e17b-b586-1e6e-aa47-f3fcdd3c660d@nvidia.com>
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On 03/11/16 00:18, Kirti Wankhede wrote:
>
>
> On 11/2/2016 6:30 PM, Jike Song wrote:
>> 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);
get_task_mm() increments mm_users which is basically a number of userspaces
holding the reference to mm. As this case it is not a userspace, mm_count
needs to be incremented imho.
>>>
>>> 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?
>>
>
> If the process is terminated by SIGKILL, as Alexey mentioned in this
> mail thread earlier exit_mm() is called first and then all files are
> closed. From exit_mm(), task->mm is set to NULL. So from teardown path,
> we should call get_task_mm(task)
... which will return NULL, no?
> to get current status intsead of using
> stale pointer.
If you increment either mm_users or mm_count at the exact place where you
want to cache task pointer, why would mm pointer become stale until you do
mmdrop() or mmput()?
--
Alexey
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next prev parent reply other threads:[~2016-11-03 4:30 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-17 21:22 [PATCH v9 00/12] Add Mediated device support Kirti Wankhede
2016-10-17 21:22 ` [PATCH v9 01/12] vfio: Mediated device Core driver Kirti Wankhede
2016-10-18 23:16 ` Alex Williamson
2016-10-19 19:16 ` Kirti Wankhede
2016-10-19 22:20 ` Alex Williamson
2016-10-20 7:23 ` Jike Song
2016-10-20 17:12 ` Alex Williamson
2016-10-21 2:41 ` Jike Song
2016-10-27 5:56 ` Jike Song
2016-10-26 6:52 ` Tian, Kevin
2016-10-26 14:58 ` Kirti Wankhede
2016-10-17 21:22 ` [PATCH v9 02/12] vfio: VFIO based driver for Mediated devices Kirti Wankhede
2016-10-26 6:57 ` Tian, Kevin
2016-10-26 15:01 ` Kirti Wankhede
2016-10-17 21:22 ` [PATCH v9 03/12] vfio: Rearrange functions to get vfio_group from dev Kirti Wankhede
2016-10-19 17:26 ` Alex Williamson
2016-10-17 21:22 ` [PATCH v9 04/12] vfio iommu: Add support for mediated devices Kirti Wankhede
2016-10-19 21:02 ` Alex Williamson
2016-10-20 20:17 ` Kirti Wankhede
2016-10-24 2:32 ` Alex Williamson
2016-10-26 7:19 ` Tian, Kevin
2016-10-26 15:06 ` Kirti Wankhede
2016-10-26 7:53 ` Tian, Kevin
2016-10-26 15:16 ` Alex Williamson
2016-10-26 7:54 ` Tian, Kevin
2016-10-26 15:19 ` Alex Williamson
2016-10-21 7:49 ` Jike Song
2016-10-21 14:36 ` Alex Williamson
2016-10-24 10:35 ` Kirti Wankhede
2016-10-27 7:20 ` [Qemu-devel] " Alexey Kardashevskiy
2016-10-27 12:31 ` Kirti Wankhede
2016-10-27 14:30 ` Alex Williamson
2016-10-27 15:59 ` Kirti Wankhede
2016-10-28 2:18 ` Alexey Kardashevskiy
2016-11-01 14:01 ` Kirti Wankhede
2016-11-02 1:24 ` Alexey Kardashevskiy
2016-11-02 3:29 ` Kirti Wankhede
2016-11-02 4:09 ` Alexey Kardashevskiy
2016-11-02 12:21 ` Jike Song
2016-11-02 12:41 ` Kirti Wankhede
2016-11-02 13:00 ` Jike Song
2016-11-02 13:18 ` Kirti Wankhede
2016-11-02 13:35 ` Jike Song
2016-11-03 4:29 ` Alexey Kardashevskiy [this message]
2016-10-17 21:22 ` [PATCH v9 05/12] vfio: Introduce common function to add capabilities Kirti Wankhede
2016-10-20 19:24 ` Alex Williamson
2016-10-24 21:27 ` Kirti Wankhede
2016-10-24 21:39 ` Alex Williamson
2016-10-17 21:22 ` [PATCH v9 06/12] vfio_pci: Update vfio_pci to use vfio_info_add_capability() Kirti Wankhede
2016-10-20 19:24 ` Alex Williamson
2016-10-24 21:22 ` Kirti Wankhede
2016-10-24 21:37 ` Alex Williamson
2016-10-17 21:22 ` [PATCH v9 07/12] vfio: Introduce vfio_set_irqs_validate_and_prepare() Kirti Wankhede
2016-10-17 21:22 ` [PATCH v9 08/12] vfio_pci: Updated to use vfio_set_irqs_validate_and_prepare() Kirti Wankhede
2016-10-17 21:22 ` [PATCH v9 09/12] vfio_platform: " Kirti Wankhede
2016-10-17 21:22 ` [PATCH v9 10/12] vfio: Add function to get device_api string from vfio_device_info.flags Kirti Wankhede
2016-10-20 19:34 ` Alex Williamson
2016-10-20 20:29 ` Kirti Wankhede
2016-10-20 21:05 ` Alex Williamson
2016-10-20 21:14 ` Kirti Wankhede
2016-10-20 21:22 ` Alex Williamson
2016-10-21 3:00 ` Kirti Wankhede
2016-10-21 3:20 ` Alex Williamson
2016-10-17 21:22 ` [PATCH v9 11/12] docs: Add Documentation for Mediated devices Kirti Wankhede
2016-10-25 16:17 ` Alex Williamson
2016-10-17 21:22 ` [PATCH v9 12/12] docs: Sample driver to demonstrate how to use Mediated device framework Kirti Wankhede
[not found] ` <20161018025411.GA22572@bjsdjshi@linux.vnet.ibm.com>
2016-10-18 17:17 ` Alex Williamson
2016-10-19 19:19 ` Kirti Wankhede
2016-10-17 21:41 ` [PATCH v9 00/12] Add Mediated device support Alex Williamson
2016-10-24 7:07 ` Jike Song
2016-12-05 17:44 ` Gerd Hoffmann
2016-12-06 2:24 ` Jike Song
2016-12-07 14:40 ` Gerd Hoffmann
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