From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751204AbdL3VWr (ORCPT ); Sat, 30 Dec 2017 16:22:47 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:35229 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750968AbdL3VWL (ORCPT ); Sat, 30 Dec 2017 16:22:11 -0500 Message-Id: <20171230211829.679325424@linutronix.de> User-Agent: quilt/0.63-1 Date: Sat, 30 Dec 2017 22:13:54 +0100 From: Thomas Gleixner To: LKML Cc: Linus Torvalds , x86@kernel.org, Andy Lutomirski , Dave Hansen , Peter Zijlstra , Borislav Petkov , Dominik Brodowski Subject: [patch 3/3] x86/mm: Remove preempt_disable/enable() from __native_flush_tlb() References: <20171230211351.980176980@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=x86-mm--Remove-preempt_disable-enable---from-__native_tlb_flush--.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The preempt_disable/enable() pair in __native_flush_tlb() was added in commit 5cf0791da5c1 ("x86/mm: Disable preemption during CR3 read+write") to protect the UP variant of flush_tlb_mm_range(). That preempt_disable/enable() pair should have been added to the UP variant of flush_tlb_mm_range() instead. The UP variant was removed with commit ce4a4e565f52 ("x86/mm: Remove the UP asm/tlbflush.h code, always use the (formerly) SMP code"), but the preempt_disable/enable() pair stayed around. The latest change to __native_flush_tlb() in commit 6fd166aae78c ("x86/mm: Use/Fix PCID to optimize user/kernel switches") added an access to a per cpu variable outside the preempt disabled regions which makes no sense at all. __native_flush_tlb() must always be called with at least preemption disabled. Remove the preempt_disable/enable() pair and add a WARN_ON_ONCE() to catch bad callers independent of the smp_processor_id() debugging. Signed-off-by: Thomas Gleixner --- arch/x86/include/asm/tlbflush.h | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -345,15 +345,17 @@ static inline void invalidate_user_asid( */ static inline void __native_flush_tlb(void) { - invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid)); /* - * If current->mm == NULL then we borrow a mm which may change - * during a task switch and therefore we must not be preempted - * while we write CR3 back: + * Preemption or interrupts must be disabled to protect the access + * to the per cpu variable and to prevent being preempted between + * read_cr3() and write_cr3(). */ - preempt_disable(); + WARN_ON_ONCE(preemptible()); + + invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid)); + + /* If current->mm == NULL then the read_cr3() "borrows" a mm */ native_write_cr3(__native_read_cr3()); - preempt_enable(); } /*