linux-kernel - Re: [PATCH v3] kcmp: Support selection of SYS_kcmp without CHECKPOINT

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Date:   Fri, 12 Feb 2021 15:01:16 +0100
From:   Michel Dänzer <michel@...nzer.net>
To:     Emil Velikov <emil.l.velikov@...il.com>,
        Chris Wilson <chris@...is-wilson.co.uk>
Cc:     Will Drewry <wad@...omium.org>, Kees Cook <keescook@...omium.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        "# 3.13+" <stable@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3] kcmp: Support selection of SYS_kcmp without
 CHECKPOINT_RESTORE

On 2021-02-12 1:57 p.m., Emil Velikov wrote:
> On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@...is-wilson.co.uk> wrote:
>>
>> Userspace has discovered the functionality offered by SYS_kcmp and has
>> started to depend upon it. In particular, Mesa uses SYS_kcmp for
>> os_same_file_description() in order to identify when two fd (e.g. device
>> or dmabuf)
> 
> As you rightfully point out, SYS_kcmp is a bit of a two edged sword.
> While you mention the CONFIG issue, there is also a portability aspect
> (mesa runs on more than just linux) and as well as sandbox filtering
> of the extra syscall.
> 
> Last time I looked, the latter was still an issue and mesa was using
> SYS_kcmp to compare device node fds.
> A far shorter and more portable solution is possible, so let me
> prepare a Mesa patch.

Make sure to read my comments on 
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6881 first. :)


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer