From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
"Krzysztof Mazur" <krzysiek@podlesie.net>,
"Krzysztof Olędzki" <ole@ans.pl>, "Arnd Bergmann" <arnd@arndb.de>,
"Josh Poimboeuf" <jpoimboe@redhat.com>
Subject: Re: [PATCH v2 4/4] x86/fpu/64: Don't FNINIT in kernel_fpu_begin()
Date: Wed, 20 Jan 2021 11:07:11 +0100 [thread overview]
Message-ID: <YAgAz4qYESIv8iNR@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <803d45a172a25314fdaec0a01aada8333d55df4e.1611077835.git.luto@kernel.org>
On Tue, Jan 19, 2021 at 09:39:02AM -0800, Andy Lutomirski wrote:
> The remaining callers of kernel_fpu_begin() in 64-bit kernels don't use 387
> instructions, so there's no need to sanitize the FPU state. Skip it to get
> most of the performance we lost back.
>
> Reported-by: Krzysztof Olędzki <ole@ans.pl>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/include/asm/fpu/api.h | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
> index 38f4936045ab..435bc59d539b 100644
> --- a/arch/x86/include/asm/fpu/api.h
> +++ b/arch/x86/include/asm/fpu/api.h
> @@ -32,7 +32,19 @@ extern void fpregs_mark_activate(void);
> /* Code that is unaware of kernel_fpu_begin_mask() can use this */
> static inline void kernel_fpu_begin(void)
> {
> +#ifdef CONFIG_X86_64
> + /*
> + * Any 64-bit code that uses 387 instructions must explicitly request
> + * KFPU_387.
> + */
> + kernel_fpu_begin_mask(KFPU_MXCSR);
I'm also still sitting on this:
git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git x86/fpu
what do we do with that?
next prev parent reply other threads:[~2021-01-20 10:30 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 17:38 [PATCH v2 0/4] x86/fpu: Reduce unnecessary FNINIT and MXCSR usage Andy Lutomirski
2021-01-19 17:38 ` [PATCH v2 1/4] x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state Andy Lutomirski
2021-01-19 19:34 ` Sean Christopherson
2021-01-20 11:53 ` Borislav Petkov
2021-01-20 12:19 ` Andy Lutomirski
2021-01-19 17:39 ` [PATCH v2 2/4] x86/mmx: Use KFPU_387 for MMX string operations Andy Lutomirski
2021-01-20 18:18 ` Borislav Petkov
2021-01-19 17:39 ` [PATCH v2 3/4] x86/fpu: Make the EFI FPU calling convention explicit Andy Lutomirski
2021-01-19 17:39 ` [PATCH v2 4/4] x86/fpu/64: Don't FNINIT in kernel_fpu_begin() Andy Lutomirski
2021-01-20 10:07 ` Peter Zijlstra [this message]
2021-01-20 18:28 ` Borislav Petkov
2021-01-20 7:51 ` [PATCH v2 0/4] x86/fpu: Reduce unnecessary FNINIT and MXCSR usage Krzysztof Olędzki
2021-01-21 5:03 ` Andy Lutomirski
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