linux-kernel - Re: [RFC PATCH 4/6] x86/fpu: Fix "x86/fpu: Legacy x87 FPU detected" message

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Message-ID: <CALCETrUQ5tR23C=JptP=gxGQ_fbgUOG3pSWcrgOqsHZDJLXQFg@mail.gmail.com>
Date:   Tue, 6 Dec 2016 09:59:56 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Matthew Whitehead <tedheadster@...il.com>
Subject: Re: [RFC PATCH 4/6] x86/fpu: Fix "x86/fpu: Legacy x87 FPU detected" message

On Tue, Dec 6, 2016 at 1:24 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Mon, Dec 05, 2016 at 05:01:13PM -0800, Andy Lutomirski wrote:
>> That message isn't at all clear -- what does "Legacy x87" even
>> mean?
>>
>> Clarify it.  If there's no FPU, say "x86/fpu: No FPU detected".  If
>> there's an FPU that doesn't have XSAVE, say "x86/fpu: Pre-XSAVE x87
>> FPU detected".
>>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> ---
>>  arch/x86/kernel/fpu/xstate.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
>> index 1d7770447b3e..2d592b1c75e4 100644
>> --- a/arch/x86/kernel/fpu/xstate.c
>> +++ b/arch/x86/kernel/fpu/xstate.c
>> @@ -705,8 +705,13 @@ void __init fpu__init_system_xstate(void)
>>       WARN_ON_FPU(!on_boot_cpu);
>>       on_boot_cpu = 0;
>>
>> +     if (!boot_cpu_has(X86_FEATURE_FPU)) {
>> +             pr_info("x86/fpu: No FPU detected.\n");
>> +             return;
>> +     }
>> +
>>       if (!boot_cpu_has(X86_FEATURE_XSAVE)) {
>> -             pr_info("x86/fpu: Legacy x87 FPU detected.\n");
>> +             pr_info("x86/fpu: Pre-XSAVE x87 FPU detected.\n");
>
> Well, there's also FXSAVE and FSAVE. The legacy thing kinda made sense
> to me here.
>
> Maybe say something like this:
>
>         pr_info("x86/fpu: FPU detected: FSAVE|FXSAVE|XSAVE support\n", ...
>
> and use X86_FEATURE_XSAVE and X86_FEATURE_FXSR to print the respective
> *SAVE string...? FSAVE we issue by default.

I did something like this for FSAVE vs FXSAVE.  XSAVE has its own pile
of printouts and I don't feel like I need to add another.

>
> Hmm.
>
> --
> Regards/Gruss,
>     Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.



-- 
Andy Lutomirski
AMA Capital Management, LLC