From: Andy Lutomirski <luto@kernel.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
X86 ML <x86@kernel.org>,
jpa@kernelbug.mail.kapsi.fi, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] x86/fpu: Reset MXCSR to default in kernel_fpu_begin()
Date: Mon, 22 Jun 2020 11:40:38 -0700 [thread overview]
Message-ID: <CALCETrUT1_WVjMbPZhUcX9sjFvLBZKCc2fxeJJsD940k1Ajyrw@mail.gmail.com> (raw)
In-Reply-To: <ef327682-7e9f-5652-1664-3e201ac38f60@intel.com>
On Mon, Jun 22, 2020 at 11:38 AM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 6/22/20 11:33 AM, Andy Lutomirski wrote:
> > Suppose you do:
> >
> > double x = 1.0;
> >
> > kernel_fpu_begin();
> >
> > x += 2.0;
> >
> > We want to make sure that GCC puts things in the right order. I
> > suppose that even a memory clobber is insufficient here, though.
>
> Even with CONFIG_PREEMPT disabled, we still have:
>
> #define preempt_disable() barrier()
>
> I don't see us supporting preemptible kernel_fpu regions any time soon,
> so shouldn't this be sufficient now and for a long time?
That's on the wrong end of the function. It'sL
preempt_disable();
LDMXCSR;
<-- some kind of barrier here might be nice
--Andy
next prev parent reply other threads:[~2020-06-22 18:40 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 17:41 [PATCH 0/2] x86/FPU: FPU sanitization for in-kernel use Borislav Petkov
2020-06-19 17:41 ` [PATCH 1/2] x86/fpu: Reset MXCSR to default in kernel_fpu_begin() Borislav Petkov
2020-06-19 18:01 ` Andy Lutomirski
2020-06-22 17:09 ` Borislav Petkov
2020-06-22 18:33 ` Andy Lutomirski
2020-06-22 18:36 ` Petteri Aimonen
2020-06-22 18:38 ` Dave Hansen
2020-06-22 18:40 ` Andy Lutomirski [this message]
2020-06-22 18:59 ` Borislav Petkov
2020-06-19 17:41 ` [PATCH 2/2] selftests/fpu: Add an FPU selftest Borislav Petkov
2020-06-19 18:00 ` Andy Lutomirski
2020-06-22 17:12 ` Borislav Petkov
2020-06-22 18:26 ` Andy Lutomirski
2020-06-22 19:01 ` Borislav Petkov
[not found] ` <B4D00859-000A-4F8C-8CFB-45B9BBCCA16D@amacapital.net>
2020-06-23 10:28 ` Borislav Petkov
2020-06-23 18:22 ` Andy Lutomirski
2020-06-23 18:47 ` Borislav Petkov
2020-06-23 19:07 ` Nick Desaulniers
2020-06-23 19:13 ` Borislav Petkov
2020-06-23 20:58 ` Nick Desaulniers
2020-06-23 21:32 ` Borislav Petkov
2020-06-20 19:55 ` kernel test robot
2020-06-22 17:04 ` Borislav Petkov
2020-06-22 18:15 ` Nick Desaulniers
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