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

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Date:   Tue, 6 Dec 2016 10:24:24 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     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 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.

Hmm.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.