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

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Message-Id: <301D30B5-26F7-454B-8C0C-A5DFC73222CF@amacapital.net>
Date:   Thu, 11 Jun 2020 07:19:53 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Petteri Aimonen <jpa@....mail.kapsi.fi>,
        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 Jun 11, 2020, at 2:18 AM, Borislav Petkov <bp@...en8.de> wrote:
> 
> 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.

Seems good to me. Let’s have at least two users before we go nuts with the architecture :)

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>    Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette