From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751971AbdJRQ2d (ORCPT ); Wed, 18 Oct 2017 12:28:33 -0400 Received: from terminus.zytor.com ([65.50.211.136]:57427 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751854AbdJRQ23 (ORCPT ); Wed, 18 Oct 2017 12:28:29 -0400 Date: Wed, 18 Oct 2017 09:23:53 -0700 From: tip-bot for Andy Lutomirski Message-ID: Cc: peterz@infradead.org, tglx@linutronix.de, mingo@kernel.org, torvalds@linux-foundation.org, luto@kernel.org, hpa@zytor.com, bp@alien8.de, linux-kernel@vger.kernel.org Reply-To: mingo@kernel.org, torvalds@linux-foundation.org, luto@kernel.org, tglx@linutronix.de, peterz@infradead.org, linux-kernel@vger.kernel.org, bp@alien8.de, hpa@zytor.com In-Reply-To: <154ef95428d4592596b6e98b0af1d2747d6cfbf8.1508000261.git.luto@kernel.org> References: <154ef95428d4592596b6e98b0af1d2747d6cfbf8.1508000261.git.luto@kernel.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/mm: Tidy up "x86/mm: Flush more aggressively in lazy TLB mode" Git-Commit-ID: 4e57b94664fef55aa71cac33b4632fdfdd52b695 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 4e57b94664fef55aa71cac33b4632fdfdd52b695 Gitweb: https://git.kernel.org/tip/4e57b94664fef55aa71cac33b4632fdfdd52b695 Author: Andy Lutomirski AuthorDate: Sat, 14 Oct 2017 09:59:50 -0700 Committer: Ingo Molnar CommitDate: Wed, 18 Oct 2017 15:25:02 +0200 x86/mm: Tidy up "x86/mm: Flush more aggressively in lazy TLB mode" Due to timezones, commit: b956575bed91 ("x86/mm: Flush more aggressively in lazy TLB mode") was an outdated patch that well tested and fixed the bug but didn't address Borislav's review comments. Tidy it up: - The name "tlb_use_lazy_mode()" was highly confusing. Change it to "tlb_defer_switch_to_init_mm()", which describes what it actually means. - Move the static_branch crap into a helper. - Improve comments. Actually removing the debugfs option is in the next patch. Reported-by: Borislav Petkov Signed-off-by: Andy Lutomirski Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: b956575bed91 ("x86/mm: Flush more aggressively in lazy TLB mode") Link: http://lkml.kernel.org/r/154ef95428d4592596b6e98b0af1d2747d6cfbf8.1508000261.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/tlbflush.h | 7 ++++++- arch/x86/mm/tlb.c | 30 ++++++++++++++++++------------ 2 files changed, 24 insertions(+), 13 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index d362161..0d4a1bb 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -87,7 +87,12 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) * to init_mm when we switch to a kernel thread (e.g. the idle thread). If * it's false, then we immediately switch CR3 when entering a kernel thread. */ -DECLARE_STATIC_KEY_TRUE(tlb_use_lazy_mode); +DECLARE_STATIC_KEY_TRUE(__tlb_defer_switch_to_init_mm); + +static inline bool tlb_defer_switch_to_init_mm(void) +{ + return static_branch_unlikely(&__tlb_defer_switch_to_init_mm); +} /* * 6 because 6 should be plenty and struct tlb_state will fit in diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 7db23f9..5ee3b59 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -30,7 +30,7 @@ atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1); -DEFINE_STATIC_KEY_TRUE(tlb_use_lazy_mode); +DEFINE_STATIC_KEY_TRUE(__tlb_defer_switch_to_init_mm); static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen, u16 *new_asid, bool *need_flush) @@ -213,6 +213,9 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, } /* + * Please ignore the name of this function. It should be called + * switch_to_kernel_thread(). + * * enter_lazy_tlb() is a hint from the scheduler that we are entering a * kernel thread or other context without an mm. Acceptable implementations * include doing nothing whatsoever, switching to init_mm, or various clever @@ -227,7 +230,7 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm) return; - if (static_branch_unlikely(&tlb_use_lazy_mode)) { + if (tlb_defer_switch_to_init_mm()) { /* * There's a significant optimization that may be possible * here. We have accurate enough TLB flush tracking that we @@ -632,7 +635,8 @@ static ssize_t tlblazy_read_file(struct file *file, char __user *user_buf, { char buf[2]; - buf[0] = static_branch_likely(&tlb_use_lazy_mode) ? '1' : '0'; + buf[0] = static_branch_likely(&__tlb_defer_switch_to_init_mm) + ? '1' : '0'; buf[1] = '\n'; return simple_read_from_buffer(user_buf, count, ppos, buf, 2); @@ -647,9 +651,9 @@ static ssize_t tlblazy_write_file(struct file *file, return -EINVAL; if (val) - static_branch_enable(&tlb_use_lazy_mode); + static_branch_enable(&__tlb_defer_switch_to_init_mm); else - static_branch_disable(&tlb_use_lazy_mode); + static_branch_disable(&__tlb_defer_switch_to_init_mm); return count; } @@ -660,23 +664,25 @@ static const struct file_operations fops_tlblazy = { .llseek = default_llseek, }; -static int __init init_tlb_use_lazy_mode(void) +static int __init init_tlblazy(void) { if (boot_cpu_has(X86_FEATURE_PCID)) { /* - * Heuristic: with PCID on, switching to and from - * init_mm is reasonably fast, but remote flush IPIs - * as expensive as ever, so turn off lazy TLB mode. + * If we have PCID, then switching to init_mm is reasonably + * fast. If we don't have PCID, then switching to init_mm is + * quite slow, so we default to trying to defer it in the + * hopes that we can avoid it entirely. The latter approach + * runs the risk of receiving otherwise unnecessary IPIs. * * We can't do this in setup_pcid() because static keys * haven't been initialized yet, and it would blow up * badly. */ - static_branch_disable(&tlb_use_lazy_mode); + static_branch_disable(&__tlb_defer_switch_to_init_mm); } - debugfs_create_file("tlb_use_lazy_mode", S_IRUSR | S_IWUSR, + debugfs_create_file("tlb_defer_switch_to_init_mm", S_IRUSR | S_IWUSR, arch_debugfs_dir, NULL, &fops_tlblazy); return 0; } -late_initcall(init_tlb_use_lazy_mode); +late_initcall(init_tlblazy);