linux-kernel - Re: [PATCH] arch/x86: reset MXCSR to default in kernel_fpu

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Message-ID: <20200611091822.GA30352@zn.tnic>
Date:   Thu, 11 Jun 2020 11:18:22 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Petteri Aimonen <jpa@....mail.kapsi.fi>
Cc:     Andy Lutomirski <luto@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86-ml <x86@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arch/x86: reset MXCSR to default in kernel_fpu_begin()

On Thu, Jun 11, 2020 at 10:36:08AM +0300, Petteri Aimonen wrote:
> Hi,
> 
> > How about putting the file you frob in
> > /sys/kernel/debug/selftest_helpers/something_or_other.  The idea would
> > be that /sys/kernel/debug/selftest_helpers would be a general place
> > for kernel helpers needed to make selftests work.
> 
> Seems like this is the consensus for now.
> 
> Any opinions on whether the module should remove "selftest_helpers"
> directory on unloading, or not?
> 
> 1) Removing would break if other test modules will use the same dir.
> 2) Not removing will leave the directory dangling.
> 3) Remove only if empty is one option, though I'm unsure how to
>    cleanly check if debugfs directory is empty.
> 4) E.g. /sys/kernel/debug/x86/ is created centrally and a symbol is
>    exported for its dentry. But I'm not sure if it really makes sense
>    to add another exported symbol just for selftest_helpers.

I'd say you do the simple thing and cleanup after you're done, i.e.,
remove the dir. When something else starts using it, then it would need
to be taught to deal with multiple users.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette