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From: Minchan Kim <minchan@kernel.org>
To: InKi Dae <daeinki@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
	Jerome Glisse <j.glisse@gmail.com>,
	Inki Dae <inki.dae@samsung.com>,
	airlied@linux.ie, dri-devel@lists.freedesktop.org,
	kyungmin.park@samsung.com, sw0312.kim@samsung.com,
	linux-mm@kvack.org
Subject: Re: [PATCH 2/2 v3] drm/exynos: added userptr feature.
Date: Mon, 14 May 2012 13:29:27 +0900	[thread overview]
Message-ID: <4FB08A27.2040503@kernel.org> (raw)
In-Reply-To: <CAAQKjZPvLXYK5e385QE7HzmKqfUJr9G3+0HVvLeiXDG+yLDx+A@mail.gmail.com>

On 05/12/2012 01:48 PM, InKi Dae wrote:

> 2012/5/12 KOSAKI Motohiro <kosaki.motohiro@gmail.com>:
>> On Fri, May 11, 2012 at 7:29 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
>>> On Fri, May 11, 2012 at 6:59 PM, KOSAKI Motohiro
>>> <kosaki.motohiro@gmail.com> wrote:
>>>>> My point is this ioctl will be restricted to one user (Xserver if i
>>>>> understand) and only this user, there is no fork in it so no need to
>>>>> worry about fork, just setting the vma as locked will be enough.
>>>>>
>>>>> But i don't want people reading this driver suddenly think that what
>>>>> it's doing is ok, it's not, it's hack and can never make to work
>>>>> properly on a general case, that's why it needs a big comment stating,
>>>>> stressing that. I just wanted to make sure Inki and Kyungmin
>>>>> understood that this kind of ioctl should be restricted to carefully
>>>>> selected user and that there is no way to make it general or reliable
>>>>> outside that.
>>>>
>>>>
>>>> first off, I'm not drm guy and then I don't intend to insist you. but if
>>>> application don't use fork, get_user_pages() has no downside. I guess we
>>>> don't need VM_LOCKED hack.
>>>>
>>>> but again, up to drm folks.
>>>
>>> You need the VM_LOCKED hack to mare sure that the xorg vma still point
>>> to the same page, afaict with get_user_pages pages can be migrated out
>>> of the anonymous vma so the vma might point to new page, while old
>>> page are still in use by the gpu and not recycle until their refcount
>>> drop to 0.
>>
>> afaik, get_user_pages() prevent page migration. (see
>> migrate_page_move_mapping). but mlock doesn't.
> 
> 
> I'd like to make sure some points before preparing next patch to
> userptr feature.
> 
> in case that userptr ioctl can be accessed by user.
> 1. all the pages from get_user_pages can't be migrated by CMA and also


Yes. I already mentioned it.

> it doesn't need VM_LOCKED or VM_RESERVED flag.


Yes, if you just use that flag to prevent migration.

> 
> 2. if VM_DONTCOPY is set to vma->flags then all the pages to this vma
> are safe from being COW.


Yes.

> 
> 3. userptr ioctl  has limited size and the limited size can be changed
> by only root user. this is for preventing from dropping system
> performance by malicious software.


IMHO, looks good to me but need answer from DRM guy on the question.

> 
> with above actions taken, are there something we didn't care? if so,
> we will preparing next path for the userptr ioctl to be accessed by
> only root user. this means that this feature is used by only X Server
> but isn't used by any users. so we are going to wait something
> resolved fully. of course, as Jerome said, we wil add big comments
> describing this feature enough to next patch.
> 
> Thanks,
> Inki Dae
> 
> --
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> 



-- 
Kind regards,
Minchan Kim

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
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Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply	other threads:[~2012-05-14  4:29 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1335188594-17454-4-git-send-email-inki.dae@samsung.com>
     [not found] ` <1336544259-17222-1-git-send-email-inki.dae@samsung.com>
     [not found]   ` <1336544259-17222-3-git-send-email-inki.dae@samsung.com>
2012-05-09 14:45     ` [PATCH 2/2 v3] drm/exynos: added userptr feature Jerome Glisse
2012-05-09 18:32       ` Jerome Glisse
2012-05-10  2:44         ` Inki Dae
2012-05-10 15:05           ` Jerome Glisse
2012-05-10 15:31             ` Daniel Vetter
2012-05-10 15:52               ` Jerome Glisse
2012-05-11  1:47                 ` Inki Dae
2012-05-11  2:08                   ` Minchan Kim
2012-05-10  1:39       ` Inki Dae
2012-05-10  4:58         ` Minchan Kim
2012-05-10  6:53           ` KOSAKI Motohiro
2012-05-10  7:27             ` Minchan Kim
2012-05-10  7:31               ` Kyungmin Park
2012-05-10  7:56                 ` Minchan Kim
2012-05-10  7:58                   ` Minchan Kim
2012-05-10  6:57           ` Inki Dae
2012-05-10  7:05             ` Minchan Kim
2012-05-10  7:59               ` InKi Dae
2012-05-10  8:11                 ` Minchan Kim
2012-05-10  8:44                   ` Inki Dae
2012-05-10 17:53                     ` KOSAKI Motohiro
2012-05-11  0:50                       ` Minchan Kim
2012-05-11  2:51                         ` KOSAKI Motohiro
2012-05-11  3:01                           ` Jerome Glisse
2012-05-11 21:20                             ` KOSAKI Motohiro
2012-05-11 22:22                               ` Jerome Glisse
2012-05-11 22:59                                 ` KOSAKI Motohiro
2012-05-11 23:29                                   ` Jerome Glisse
2012-05-11 23:39                                     ` KOSAKI Motohiro
2012-05-12  4:48                                       ` InKi Dae
2012-05-14  4:29                                         ` Minchan Kim [this message]
     [not found]   ` <1336976268-14328-1-git-send-email-inki.dae@samsung.com>
2012-05-14  8:12     ` [PATCH 0/2 v4] " Inki Dae
     [not found]     ` <1336976268-14328-2-git-send-email-inki.dae@samsung.com>
2012-05-14  8:12       ` [PATCH 1/2 v4] drm/exynos: added userptr limit ioctl Inki Dae
     [not found]     ` <1336976268-14328-3-git-send-email-inki.dae@samsung.com>
     [not found]       ` <CAHGf_=qv45_uuO_JWMXOQp4VymyOxVq76rGXghoNMmDh7mURKQ@mail.gmail.com>
     [not found]         ` <003001cd319e$263c9230$72b5b690$%dae@samsung.com>
     [not found]           ` <4FB0AE87.60800@gmail.com>
2012-05-14  8:13             ` [PATCH 2/2 v4] drm/exynos: added userptr feature Inki Dae
     [not found]       ` <CAH3drwb13T2RXgEuauGchoZUDAgL+wrv3SR66sZNyGk_6tRTFw@mail.gmail.com>
2012-05-15  4:33         ` Inki Dae
2012-05-15 14:31           ` Jerome Glisse
2012-05-16  8:49             ` Inki Dae

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