linux-kernel - Re: [PATCH] drm/i915: Remove redundant user_access_end() from __copy_from

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Message-ID: <alpine.DEB.2.21.1907252355150.1791@nanos.tec.linutronix.de>
Date:   Thu, 25 Jul 2019 23:55:45 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] drm/i915: Remove redundant user_access_end() from
 __copy_from_user() error path

On Thu, 25 Jul 2019, Josh Poimboeuf wrote:

> Objtool reports:
> 
>   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x36: redundant UACCESS disable
> 
> __copy_from_user() already does both STAC and CLAC, so the
> user_access_end() in its error path adds an extra unnecessary CLAC.
> 
> Fixes: 0b2c8f8b6b0c ("i915: fix missing user_access_end() in page fault exception case")
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Reported-by: Sedat Dilek <sedat.dilek@...il.com>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/617
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>