From: Borislav Petkov <bp@alien8.de>
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>
Subject: Re: [PATCH 1/4] x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state
Date: Tue, 19 Jan 2021 12:08:34 +0100 [thread overview]
Message-ID: <20210119110834.GH27433@zn.tnic> (raw)
In-Reply-To: <a9630f17c5bcafbfe297a0828c7b6c78b0f6dcbe.1610950681.git.luto@kernel.org>
Just nitpicks:
On Sun, Jan 17, 2021 at 10:20:38PM -0800, Andy Lutomirski wrote:
> Currently, requesting kernel FPU access doesn't distinguish which parts of
> the extended ("FPU") state are needed. This is nice for simplicity, but
> there are a few cases in which it's suboptimal:
>
> - The vast majority of in-kernel FPU users want XMM/YMM/ZMM state but do
> not use legacy 387 state. These users want MXCSR initialized but don't
> care about the FPU control word. Skipping FNINIT would save time.
> (Empirically, FNINIT is several times slower than LDMXCSR.)
>
> - Code that wants MMX doesn't want need MXCSR or FCW initialized.
"want/need" ?
> _mmx_memcpy(), for example, can run before CR4.OSFXSR gets set, and
> initializing MXCSR will fail.
"... because LDMXCSR generates an #UD when the aforementioned CR4 bit is
not set."
> - Any future in-kernel users of XFD (eXtended Feature Disable)-capable
> dynamic states will need special handling.
>
> This patch adds a more specific API that allows callers specify exactly
s/This patch adds/Add/
> what they want.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-01-19 11:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-18 6:20 [PATCH 0/4] x86/fpu: Reduce unnecessary FNINIT and MXCSR usage Andy Lutomirski
2021-01-18 6:20 ` [PATCH 1/4] x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state Andy Lutomirski
2021-01-18 12:21 ` Peter Zijlstra
2021-01-18 14:03 ` David Laight
2021-01-19 11:08 ` Borislav Petkov [this message]
2021-01-18 6:20 ` [PATCH 2/4] x86/mmx: Use KFPU_MMX for MMX string operations Andy Lutomirski
2021-01-18 6:20 ` [PATCH 3/4] x86/fpu: Make the EFI FPU calling convention explicit Andy Lutomirski
2021-01-18 12:13 ` Borislav Petkov
2021-01-18 6:20 ` [PATCH 4/4] x86/fpu/64: Don't FNINIT in kernel_fpu_begin() Andy Lutomirski
2021-01-18 8:25 ` [PATCH 0/4] x86/fpu: Reduce unnecessary FNINIT and MXCSR usage Krzysztof Olędzki
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