From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31CDEC4332E for ; Tue, 19 Jan 2021 20:38:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E87B62310D for ; Tue, 19 Jan 2021 20:38:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729281AbhASSvc (ORCPT ); Tue, 19 Jan 2021 13:51:32 -0500 Received: from mail.kernel.org ([198.145.29.99]:49912 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730577AbhASS22 (ORCPT ); Tue, 19 Jan 2021 13:28:28 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 581F523619; Tue, 19 Jan 2021 17:39:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611077952; bh=WjGuzk/VOloUTSe9j4I7TkcwS1Dn5shgj6tFjFOY1Tc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=enImUKuJ2vCMaRte5XIMcnUHkuW/c9yusTB5UrLNAXWVnHNgJiQdDESB4y+TzTyAE NLec3OlCZAyXB/nnYcllph/98lgGF2GQiJEgYTO+zxKo8POc9gYH9sWz8BmIVmmlDR ro+Gf6zqkHDL1hDqo3lvyahPi73PZob2Ms5tF2eDHi/iIbwX+FGmo8P/QdQIThjOpY L0IAFuDK1Gr2NZ53n2ePyZhwGbMTdvIZ8/5/QxOZ4ouyOkW+bmr/hUOIqiubwd6aYJ +0jYxuy1oQAVnN8og6brwB8eeo7oHwhKuBGgQIQC7q8tOvkZcg1MltPdoU6cIBZND1 8FEaRki7rWb5g== From: Andy Lutomirski To: x86@kernel.org Cc: LKML , Krzysztof Mazur , =?UTF-8?q?Krzysztof=20Ol=C4=99dzki?= , Arnd Bergmann , Andy Lutomirski Subject: [PATCH v2 1/4] x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state Date: Tue, 19 Jan 2021 09:38:59 -0800 Message-Id: X-Mailer: git-send-email 2.29.2 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 or need MXCSR initialized. _mmx_memcpy(), for example, can run before CR4.OSFXSR gets set, and initializing MXCSR will fail. - 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 what they want. Signed-off-by: Andy Lutomirski --- arch/x86/include/asm/fpu/api.h | 15 +++++++++++++-- arch/x86/kernel/fpu/core.c | 17 +++++++++++------ 2 files changed, 24 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index dcd9503b1098..38f4936045ab 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -16,14 +16,25 @@ * Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It * disables preemption so be careful if you intend to use it for long periods * of time. - * If you intend to use the FPU in softirq you need to check first with + * If you intend to use the FPU in irq/softirq you need to check first with * irq_fpu_usable() if it is possible. */ -extern void kernel_fpu_begin(void); + +/* Kernel FPU states to initialize in kernel_fpu_begin_mask() */ +#define KFPU_387 _BITUL(0) /* 387 state will be initialized */ +#define KFPU_MXCSR _BITUL(1) /* MXCSR will be initialized */ + +extern void kernel_fpu_begin_mask(unsigned int kfpu_mask); extern void kernel_fpu_end(void); extern bool irq_fpu_usable(void); 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) +{ + kernel_fpu_begin_mask(KFPU_387 | KFPU_MXCSR); +} + /* * Use fpregs_lock() while editing CPU's FPU registers or fpu->state. * A context switch will (and softirq might) save CPU's FPU registers to diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index eb86a2b831b1..d4a71596c41e 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -121,7 +121,7 @@ int copy_fpregs_to_fpstate(struct fpu *fpu) } EXPORT_SYMBOL(copy_fpregs_to_fpstate); -void kernel_fpu_begin(void) +void kernel_fpu_begin_mask(unsigned int kfpu_mask) { preempt_disable(); @@ -141,13 +141,18 @@ void kernel_fpu_begin(void) } __cpu_invalidate_fpregs_state(); - if (boot_cpu_has(X86_FEATURE_XMM)) - ldmxcsr(MXCSR_DEFAULT); + /* Put sane initial values into the control registers. */ + if (likely(kfpu_mask & KFPU_MXCSR)) { + if (boot_cpu_has(X86_FEATURE_XMM)) + ldmxcsr(MXCSR_DEFAULT); + } - if (boot_cpu_has(X86_FEATURE_FPU)) - asm volatile ("fninit"); + if (unlikely(kfpu_mask & KFPU_387)) { + if (boot_cpu_has(X86_FEATURE_FPU)) + asm volatile ("fninit"); + } } -EXPORT_SYMBOL_GPL(kernel_fpu_begin); +EXPORT_SYMBOL_GPL(kernel_fpu_begin_mask); void kernel_fpu_end(void) { -- 2.29.2