From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753434AbeAZPJJ (ORCPT ); Fri, 26 Jan 2018 10:09:09 -0500 Received: from terminus.zytor.com ([65.50.211.136]:48613 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752024AbeAZPJH (ORCPT ); Fri, 26 Jan 2018 10:09:07 -0500 Date: Fri, 26 Jan 2018 07:06:46 -0800 From: tip-bot for Andy Lutomirski Message-ID: Cc: neil.berrington@datacore.com, luto@kernel.org, khlebnikov@yandex-team.ru, dave.hansen@intel.com, mingo@kernel.org, hpa@zytor.com, bp@alien8.de, tglx@linutronix.de, linux-kernel@vger.kernel.org Reply-To: hpa@zytor.com, bp@alien8.de, mingo@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, dave.hansen@intel.com, neil.berrington@datacore.com, luto@kernel.org, khlebnikov@yandex-team.ru In-Reply-To: <346541c56caed61abbe693d7d2742b4a380c5001.1516914529.git.luto@kernel.org> References: <346541c56caed61abbe693d7d2742b4a380c5001.1516914529.git.luto@kernel.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/mm/64: Fix vmapped stack syncing on very-large-memory 4-level systems Git-Commit-ID: 5beda7d54eafece4c974cfa9fbb9f60fb18fd20a 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: 5beda7d54eafece4c974cfa9fbb9f60fb18fd20a Gitweb: https://git.kernel.org/tip/5beda7d54eafece4c974cfa9fbb9f60fb18fd20a Author: Andy Lutomirski AuthorDate: Thu, 25 Jan 2018 13:12:14 -0800 Committer: Thomas Gleixner CommitDate: Fri, 26 Jan 2018 15:56:23 +0100 x86/mm/64: Fix vmapped stack syncing on very-large-memory 4-level systems Neil Berrington reported a double-fault on a VM with 768GB of RAM that uses large amounts of vmalloc space with PTI enabled. The cause is that load_new_mm_cr3() was never fixed to take the 5-level pgd folding code into account, so, on a 4-level kernel, the pgd synchronization logic compiles away to exactly nothing. Interestingly, the problem doesn't trigger with nopti. I assume this is because the kernel is mapped with global pages if we boot with nopti. The sequence of operations when we create a new task is that we first load its mm while still running on the old stack (which crashes if the old stack is unmapped in the new mm unless the TLB saves us), then we call prepare_switch_to(), and then we switch to the new stack. prepare_switch_to() pokes the new stack directly, which will populate the mapping through vmalloc_fault(). I assume that we're getting lucky on non-PTI systems -- the old stack's TLB entry stays alive long enough to make it all the way through prepare_switch_to() and switch_to() so that we make it to a valid stack. Fixes: b50858ce3e2a ("x86/mm/vmalloc: Add 5-level paging support") Reported-and-tested-by: Neil Berrington Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Cc: Konstantin Khlebnikov Cc: stable@vger.kernel.org Cc: Dave Hansen Cc: Borislav Petkov Link: https://lkml.kernel.org/r/346541c56caed61abbe693d7d2742b4a380c5001.1516914529.git.luto@kernel.org --- arch/x86/mm/tlb.c | 34 +++++++++++++++++++++++++++++----- 1 file changed, 29 insertions(+), 5 deletions(-) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index a156195..5bfe61a 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -151,6 +151,34 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, local_irq_restore(flags); } +static void sync_current_stack_to_mm(struct mm_struct *mm) +{ + unsigned long sp = current_stack_pointer; + pgd_t *pgd = pgd_offset(mm, sp); + + if (CONFIG_PGTABLE_LEVELS > 4) { + if (unlikely(pgd_none(*pgd))) { + pgd_t *pgd_ref = pgd_offset_k(sp); + + set_pgd(pgd, *pgd_ref); + } + } else { + /* + * "pgd" is faked. The top level entries are "p4d"s, so sync + * the p4d. This compiles to approximately the same code as + * the 5-level case. + */ + p4d_t *p4d = p4d_offset(pgd, sp); + + if (unlikely(p4d_none(*p4d))) { + pgd_t *pgd_ref = pgd_offset_k(sp); + p4d_t *p4d_ref = p4d_offset(pgd_ref, sp); + + set_p4d(p4d, *p4d_ref); + } + } +} + void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk) { @@ -226,11 +254,7 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, * mapped in the new pgd, we'll double-fault. Forcibly * map it. */ - unsigned int index = pgd_index(current_stack_pointer); - pgd_t *pgd = next->pgd + index; - - if (unlikely(pgd_none(*pgd))) - set_pgd(pgd, init_mm.pgd[index]); + sync_current_stack_to_mm(next); } /* Stop remote flushes for the previous mm */