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[2001:1868:205::9]) by mx.google.com with ESMTPS id b62si29643264pfl.65.2016.12.08.08.53.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 08 Dec 2016 08:53:19 -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 1cF1vT-0001tJ-43; Thu, 08 Dec 2016 16:52:07 +0000 Received: from mail-wm0-x232.google.com ([2a00:1450:400c:c09::232]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1cF1vM-0001eT-BV for linux-arm-kernel@lists.infradead.org; Thu, 08 Dec 2016 16:52:01 +0000 Received: by mail-wm0-x232.google.com with SMTP id g23so226032329wme.1 for ; Thu, 08 Dec 2016 08:51:39 -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=tht1YhKu+H2NyNtZTNmhtnd6ie8/JfIzg6xlUjYaXuQ=; b=OR6R29/OJuDbd6LF3bF7FBhsoF7f5vHgcJVSz0Hb76dQ2sLnpuzhVAUPIzhYq4yL3e S3ZGRMbo8G8ziX93aIO9b1n7t66k9wBjNFvSlh/HGXHnAW5vXjAbRi/H7ZbBd48YFroU lK2L5Dt1jEfLEkv3UrtXcrkIOZWUT1v0jOQW8= 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=tht1YhKu+H2NyNtZTNmhtnd6ie8/JfIzg6xlUjYaXuQ=; b=U/T7xnY8AUH4lSYjlu7qAd0gWI6Pgo7Yqkk7DKk7pqhPnNzCoCdNi3SxZenZiyMH25 30XK8Ulzn1tYtkqpXKnytcXTIztJaDSQNiKS9JqvKxvyHaIO1ThXWr4ZHmxVJXlYKkvr sSNBs5rVe8aLwHvPiij+Kun+NVhldZurSKNI2+/b6guptJ+sW21iAwmrLnTjnoMLVjcF YW5GxaXbpiwho3A98zZHwG20djaK3thxdBJEHk6Apc5aWDJajpwwE80ShbisVBB77ybz rYv8Fm9iutyXkiQi0lIc20MveTzr2ExCxZLODl1YbA3Nd7kPH4IRQP+MKNiVb3LZZnvP /agQ== X-Gm-Message-State: AKaTC032JUWD8o53FyzhqrYh1gRLP/GYuvOttnzdZ/Edjb/LkVPjEnEMmR8S/AG5DUduURNz X-Received: by 10.28.95.85 with SMTP id t82mr2957612wmb.56.1481215897834; Thu, 08 Dec 2016 08:51:37 -0800 (PST) Received: from localhost.localdomain ([105.144.52.243]) by smtp.gmail.com with ESMTPSA id x5sm37880166wje.36.2016.12.08.08.51.36 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 08 Dec 2016 08:51:37 -0800 (PST) From: Ard Biesheuvel To: linux-arm-kernel@lists.infradead.org, dave.martin@arm.com Subject: [PATCH v3] arm64: fpsimd: improve stacking logic in non-interruptible context Date: Thu, 8 Dec 2016 16:49:39 +0000 Message-Id: <1481215779-23432-1-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-20161208_085200_635040_01F0533A X-CRM114-Status: GOOD ( 16.67 ) X-Spam-Score: -2.7 (--) X-Spam-Report: SpamAssassin version 3.4.0 on bombadil.infradead.org summary: Content analysis details: (-2.7 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.7 RCVD_IN_DNSWL_LOW RBL: Sender listed at http://www.dnswl.org/, low trust [2a00:1450:400c:c09:0:0:0:232 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 --- v3: - avoid corruption by concurrent invocations of kernel_neon_begin()/_end() 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 | 47 ++++++++++++++------ 1 file changed, 33 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..536ddab9316d 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(atomic_t, 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 = atomic_inc_return(this_cpu_ptr(&kernel_neon_nesting_level)); + BUG_ON(level > 3); + + if (level > 1) { + 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 - 2], num_regs); } else { /* * Save the userland FPSIMD state if we have one and if we @@ -241,7 +256,6 @@ 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); @@ -252,13 +266,18 @@ 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 = atomic_read(this_cpu_ptr(&kernel_neon_nesting_level)); + BUG_ON(level < 1); + + if (level > 1) { + s = this_cpu_ptr(nested_fpsimdstate); + fpsimd_load_partial_state(&s[level - 2]); } + atomic_dec(this_cpu_ptr(&kernel_neon_nesting_level)); + preempt_enable(); } EXPORT_SYMBOL(kernel_neon_end);