From: Andy Lutomirski <luto@MIT.EDU>
To: Nuno Santos <nsantos@edigma.com>
Cc: Jiri Slaby <jirislaby@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: Floating point usage inside kernel
Date: Sun, 27 Nov 2011 20:00:58 -0800 [thread overview]
Message-ID: <4ED3077A.8060206@mit.edu> (raw)
In-Reply-To: <4ECFBF56.4000002@edigma.com>
On 11/25/2011 08:16 AM, Nuno Santos wrote:
> Hi Jiri,
>
> Thanks for your reply.
>
> The algorithm is a matrix transform computation to make a affine a
> geometric transform.
>
> Basicly it is based on the following functions:
>
> http://pastebin.com/YHzYuLPU
>
> Curiously I ran a test before writing this email and guest what.... is
> working!! :)
>
> But now that I have opened this question here I should ask... is it safe?
[...]
> I'm not protecting the call to the function with kernel_fpu_begin and
> kernel_fpu_end
It's not safe even if you do protect it with kernel_fpu_begin. On
x86-64, a userspace process that mucks with MXCSR can trivially cause
you to oops even if you use kernel_fpu_begin. (I'm pretty sure x86-32
has a similar issue, and I imagine that other architectures have related
issues.) This might change someday, but there are exactly zero use
cases outside staging, so don't hold your breath.
--Andy
prev parent reply other threads:[~2011-11-28 4:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <S1754322Ab1KYK6W/20111125105822Z+929@vger.kernel.org>
2011-11-25 11:14 ` Floating point usage inside kernel Nuno Santos
2011-11-25 12:08 ` Jiri Slaby
2011-11-25 16:16 ` Nuno Santos
2011-11-25 17:05 ` Paulo Marques
2011-11-25 17:46 ` Nuno Santos
2011-11-25 18:10 ` Paulo Marques
2011-11-28 10:11 ` Nuno Santos
2011-11-28 12:50 ` Paulo Marques
2011-11-28 4:00 ` Andy Lutomirski [this message]
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