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[2001:1868:205::9]) by mx.google.com with ESMTPS id 1si23464485plu.329.2016.12.07.02.16.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Dec 2016 02:16:20 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-arm-kernel-bounces+patch=linaro.org@lists.infradead.org designates 2001:1868:205::9 as permitted sender) client-ip=2001:1868:205::9; Authentication-Results: mx.google.com; dkim=neutral (body hash did not verify) header.i=@linaro.org; spf=pass (google.com: best guess record for domain of linux-arm-kernel-bounces+patch=linaro.org@lists.infradead.org designates 2001:1868:205::9 as permitted sender) smtp.mailfrom=linux-arm-kernel-bounces+patch=linaro.org@lists.infradead.org; dmarc=fail (p=NONE dis=NONE) header.from=linaro.org Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1cEZFM-0005bm-1r; Wed, 07 Dec 2016 10:14:44 +0000 Received: from mail-wj0-x22e.google.com ([2a00:1450:400c:c01::22e]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1cEZFF-0005T5-SC for linux-arm-kernel@lists.infradead.org; Wed, 07 Dec 2016 10:14:39 +0000 Received: by mail-wj0-x22e.google.com with SMTP id tg4so100781653wjb.1 for ; Wed, 07 Dec 2016 02:14:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id; bh=EAP5hCfJD27tFoaYLRKoupcDc1VAHyAWQOkjyxRufx0=; b=QVfuoj56W9ltBr7C8AfWNo3f4qNVZbso7RpZctPir2mziaUqMVQAwpjJCrexqKglSA 4l8JSCGiX6viRVgwcaANoZAPps5U+Q4+m6LqcolD68H7WbnYFPgTdOfmm/+wys0TQori 91+F7WEuU/+GzMfRkfA+zyV3pSVJceGQaIJzI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=EAP5hCfJD27tFoaYLRKoupcDc1VAHyAWQOkjyxRufx0=; b=CVWpp6o4XKKQvO0CrY/abIt4Si6R8tw3jalPyyHHtSW3LqqTXf2U9Rj3EdaCJxDe9w Dh8fFcZlIYpa9d9sJBYXndu1DJnl/lcyvg+3ocH/YaFo5fYBh8NH/6LFWBI8XXbQFF1i KcJp7PKtzKOkms0EevHVjeupwz+ul5LfWPoWsNGIqQ2BhIuv9Svxd4FezYF6c1MOPoPp 0v5PDhx9SZtFTCxHvDySCBH9OrykMmXpunY6tzdKytSI57hnygScDL3M//6x2n77jhI1 IsZLfUUXOOODvyG+p347ypIjk1Ft7nQzwybrIUW0L/R3ZF+ZEvZzoaE+vHXu55aCIvq+ preA== X-Gm-Message-State: AKaTC00swMhPYSS6daeh2HaceltiClTr3FS9176kE3apbgasM1vHpzncf1GJ+v72WgNRIFeY X-Received: by 10.194.26.133 with SMTP id l5mr59176603wjg.4.1481105654520; Wed, 07 Dec 2016 02:14:14 -0800 (PST) Received: from localhost.localdomain ([105.144.52.243]) by smtp.gmail.com with ESMTPSA id w18sm8816277wme.9.2016.12.07.02.14.12 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 07 Dec 2016 02:14:13 -0800 (PST) From: Ard Biesheuvel To: linux-arm-kernel@lists.infradead.org, dave.martin@arm.com Subject: [PATCH v2] arm64: fpsimd: improve stacking logic in non-interruptible context Date: Wed, 7 Dec 2016 10:14:08 +0000 Message-Id: <1481105648-19775-1-git-send-email-ard.biesheuvel@linaro.org> X-Mailer: git-send-email 2.7.4 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20161207_021438_293966_2D9370FF X-CRM114-Status: GOOD ( 16.58 ) X-Spam-Score: -2.0 (--) X-Spam-Report: SpamAssassin version 3.4.0 on bombadil.infradead.org summary: Content analysis details: (-2.0 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [2a00:1450:400c:c01:0:0:0:22e listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: catalin.marinas@arm.com, will.deacon@arm.com, Ard Biesheuvel MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patch=linaro.org@lists.infradead.org Currently, we allow kernel mode NEON in softirq or hardirq context by stacking and unstacking a slice of the NEON register file for each call to kernel_neon_begin() and kernel_neon_end(), respectively. Given that a) a CPU typically spends most of its time in userland, during which time no kernel mode NEON in process context is in progress, b) a CPU spends most of its time in the kernel doing other things than kernel mode NEON when it gets interrupted to perform kernel mode NEON in softirq context the stacking and subsequent unstacking is only necessary if we are interrupting a thread while it is performing kernel mode NEON in process context, which means that in all other cases, we can simply preserve the userland FPSIMD state once, and only restore it upon return to userland, even if we are being invoked from softirq or hardirq context. So instead of checking whether we are running in interrupt context, keep track of the level of nested kernel mode NEON calls in progress, and only perform the eager stack/unstack if the level exceeds 1. Signed-off-by: Ard Biesheuvel --- v2: - BUG() on unexpected values of the nesting level - relax the BUG() on num_regs>32 to a WARN, given that nothing actually breaks in that case arch/arm64/kernel/fpsimd.c | 48 ++++++++++++++------ 1 file changed, 34 insertions(+), 14 deletions(-) -- 2.7.4 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 394c61db5566..ae2c1bf569db 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -220,20 +220,35 @@ void fpsimd_flush_task_state(struct task_struct *t) #ifdef CONFIG_KERNEL_MODE_NEON -static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate); -static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate); +/* + * Although unlikely, it is possible for three kernel mode NEON contexts to + * be live at the same time: process context, softirq context and hardirq + * context. So while the userland context is stashed in the thread's fpsimd + * state structure, we need two additional levels of storage. + */ +static DEFINE_PER_CPU(struct fpsimd_partial_state, nested_fpsimdstate[2]); +static DEFINE_PER_CPU(int, kernel_neon_nesting_level); /* * Kernel-side NEON support functions */ void kernel_neon_begin_partial(u32 num_regs) { - if (in_interrupt()) { - struct fpsimd_partial_state *s = this_cpu_ptr( - in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); + struct fpsimd_partial_state *s; + int level; + + preempt_disable(); + + level = this_cpu_read(kernel_neon_nesting_level); + BUG_ON(level > 2); + + if (level > 0) { + s = this_cpu_ptr(nested_fpsimdstate); - BUG_ON(num_regs > 32); - fpsimd_save_partial_state(s, roundup(num_regs, 2)); + WARN_ON_ONCE(num_regs > 32); + num_regs = min(roundup(num_regs, 2), 32U); + + fpsimd_save_partial_state(&s[level - 1], num_regs); } else { /* * Save the userland FPSIMD state if we have one and if we @@ -241,24 +256,29 @@ void kernel_neon_begin_partial(u32 num_regs) * that there is no longer userland FPSIMD state in the * registers. */ - preempt_disable(); if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE)) fpsimd_save_state(¤t->thread.fpsimd_state); this_cpu_write(fpsimd_last_state, NULL); } + this_cpu_write(kernel_neon_nesting_level, level + 1); } EXPORT_SYMBOL(kernel_neon_begin_partial); void kernel_neon_end(void) { - if (in_interrupt()) { - struct fpsimd_partial_state *s = this_cpu_ptr( - in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); - fpsimd_load_partial_state(s); - } else { - preempt_enable(); + struct fpsimd_partial_state *s; + int level; + + level = this_cpu_read(kernel_neon_nesting_level) - 1; + BUG_ON(level < 0); + + if (level > 0) { + s = this_cpu_ptr(nested_fpsimdstate); + fpsimd_load_partial_state(&s[level - 1]); } + this_cpu_write(kernel_neon_nesting_level, level); + preempt_enable(); } EXPORT_SYMBOL(kernel_neon_end);