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From: Emil Velikov <emil.l.velikov-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: "Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>
Cc: amd-gfx mailing list
	<amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>
Subject: Re: [PATCH xf86-video-ati 5/6] Make all active CRTCs scan out an all-black framebuffer in LeaveVT
Date: Wed, 30 Aug 2017 11:27:07 +0100	[thread overview]
Message-ID: <CACvgo51bzkmjadyRqH+7quMt6VOW=tp24h3Gv3iDNdEhKDN1nQ@mail.gmail.com> (raw)
In-Reply-To: <8d6d0c04-7994-3b7a-6db6-cac8d8be3a4c-otUistvHUpPR7s880joybQ@public.gmane.org>

On 30 August 2017 at 09:04, Michel Dänzer <michel@daenzer.net> wrote:
> On 29/08/17 07:56 PM, Emil Velikov wrote:
>> On 28 August 2017 at 10:23, Michel Dänzer <michel@daenzer.net> wrote:
>>> From: Michel Dänzer <michel.daenzer@amd.com>
>>>
>>> And destroy all other FBs. This is so that other DRM masters can only
>>> get access to this all-black FB, not to any other FB we created, while
>>> we're switched away and not DRM master.
>>>
>> Isn't the issue applicable overall - be that in X, wayland compositors, other?
>
> Potentially.
>
Ack, ty.

>
>> IIRC the vmwgfx's kernel driver, which has extra locking [1] in order
>> to address that.
>> Would a similar approach like that be applicable for radeon/amdgpu?
>
> I don't see how that's related.
>
> The issue is that if the caller of DRM_IOCTL_MODE_GETFB is DRM master
> (or root, or using a DRM control device node), the ioctl returns a valid
> GEM handle for the framebuffer, so the caller can use the underlying
> buffer arbitrarily. This is handled by core DRM code, there's nothing
> kernel drivers can do about it.
>
Disclaimer: I'm might be a mile off.

vmgfx's vmw_master_check() which does the usual DRM master/control or
root checking.
There is a "Check if we were previously master, but now dropped" which
seems, perhaps too vaguely, related to what's happening here.

Admittedly I've not looked too closely at the locked_master and
associated ttm code (ttm_read_lock, etc).
But was under the impression that it is used to restrict access to the
[contents behind the] GEM handle, when DRM master is dropped.

That said, I'm silly - vmwgfx specifics in a radeon/ati thread is not
the right thing.

Thanks
Emil
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  parent reply	other threads:[~2017-08-30 10:27 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-28  9:23 [PATCH xf86-video-ati 0/6] Harden against other DRM masters Michel Dänzer
     [not found] ` <20170828092343.27742-1-michel-otUistvHUpPR7s880joybQ@public.gmane.org>
2017-08-28  9:23   ` [PATCH xf86-video-ati 1/6] Create radeon_pixmap_clear helper Michel Dänzer
2017-08-28  9:23   ` [PATCH xf86-video-ati 2/6] Create drmmode_set_mode helper Michel Dänzer
2017-08-28  9:23   ` [PATCH xf86-video-ati 3/6] Create radeon_pixmap_get_fb_ptr helper Michel Dänzer
2017-08-28  9:23   ` [PATCH xf86-video-ati 4/6] Create radeon_master_screen helper Michel Dänzer
2017-08-28  9:23   ` [PATCH xf86-video-ati 5/6] Make all active CRTCs scan out an all-black framebuffer in LeaveVT Michel Dänzer
     [not found]     ` <20170828092343.27742-6-michel-otUistvHUpPR7s880joybQ@public.gmane.org>
2017-08-29 10:56       ` Emil Velikov
     [not found]         ` <CACvgo52+5yVkKdwDMSdGnbM2C-Z-wUt3NdewP8oystW6=LVn2Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-30  8:04           ` Michel Dänzer
     [not found]             ` <8d6d0c04-7994-3b7a-6db6-cac8d8be3a4c-otUistvHUpPR7s880joybQ@public.gmane.org>
2017-08-30 10:27               ` Emil Velikov [this message]
     [not found]                 ` <CACvgo51bzkmjadyRqH+7quMt6VOW=tp24h3Gv3iDNdEhKDN1nQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-31  2:35                   ` Michel Dänzer
2017-08-28  9:23   ` [PATCH xf86-video-ati 6/6] Remove drmmode_scanout_free Michel Dänzer
2017-08-28 17:09   ` [PATCH xf86-video-ati 0/6] Harden against other DRM masters Deucher, Alexander

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