From: Jens Axboe <axboe@kernel.dk>
To: Josh Poimboeuf <jpoimboe@kernel.org>,
Phillip Potter <phil@philpotter.co.uk>
Cc: linux-kernel@vger.kernel.org, Jordy Zomer <jordyzomer@google.com>
Subject: Re: [PATCH] cdrom: Avoid barrier_nospec() in cdrom_ioctl_media_changed()
Date: Thu, 17 Oct 2024 18:33:24 -0600 [thread overview]
Message-ID: <dd1712dd-1485-417a-81cc-482d7dd26a11@kernel.dk> (raw)
In-Reply-To: <1d86f4d9d8fba68e5ca64cdeac2451b95a8bf872.1729202937.git.jpoimboe@kernel.org>
On 10/17/24 4:09 PM, Josh Poimboeuf wrote:
> The barrier_nospec() after the array bounds check is overkill and
> painfully slow for arches which implement it.
>
> Furthermore, most arches don't implement it, so they remain exposed to
> Spectre v1 (which can affect pretty much any CPU with branch
> prediction).
>
> Instead, clamp the user pointer to a valid range so it's guaranteed to
> be a valid array index even when the bounds check mispredicts.
It's a cdrom, and media change detection to be more specific. I really
don't think anyone would care about performance here, it's not even
a hot path for a cdrom driver. That said, I don't disagree with
the change, just don't think it'll make one iota of difference
in the real world.
--
Jens Axboe
next prev parent reply other threads:[~2024-10-18 0:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-17 22:09 Josh Poimboeuf
2024-10-18 0:33 ` Jens Axboe [this message]
2024-10-18 0:52 ` Josh Poimboeuf
2024-10-18 1:10 ` Jens Axboe
2024-10-18 1:47 ` Jens Axboe
2024-10-18 10:31 ` Phillip Potter
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