Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BFEFBC433F5 for ; Fri, 10 Dec 2021 09:54:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239682AbhLJJ6S (ORCPT ); Fri, 10 Dec 2021 04:58:18 -0500 Received: from foss.arm.com ([217.140.110.172]:39922 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239671AbhLJJ6R (ORCPT ); Fri, 10 Dec 2021 04:58:17 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E84BB1FB; Fri, 10 Dec 2021 01:54:42 -0800 (PST) Received: from entos-thunderx2-desktop.shanghai.arm.com (entos-thunderx2-desktop.shanghai.arm.com [10.169.212.208]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 138643F73B; Fri, 10 Dec 2021 01:54:38 -0800 (PST) From: Jianyong Wu To: catalin.marinas@arm.com, will@kernel.org, anshuman.khandual@arm.com, akpm@linux-foundation.org Cc: ardb@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, david@redhat.com, gshan@redhat.com, justin.he@arm.com, jianyong.wu@arm.com, nd@arm.com Subject: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping Date: Fri, 10 Dec 2021 17:54:32 +0800 Message-Id: <20211210095432.51798-1-jianyong.wu@arm.com> X-Mailer: git-send-email 2.17.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org fixmap is a global resource and is used recursively in create pud mapping. It may lead to race condition when alloc_init_pud is called concurrently. Fox example: alloc_init_pud is called when kernel_init. If memory hotplug thread, which will also call alloc_init_pud, happens during kernel_init, the race for fixmap occurs. The race condition flow can be: *************** begin ************** kerenl_init thread virtio-mem workqueue thread ================== ======== ================== alloc_init_pud(...) pudp = pud_set_fixmap_offset(..) alloc_init_pud(...) ... ... READ_ONCE(*pudp) //OK! pudp = pud_set_fixmap_offset( ... ... pud_clear_fixmap() //fixmap break READ_ONCE(*pudp) //CRASH! **************** end *************** Hence, a spin lock is introduced to protect the fixmap during create pdg mapping. Signed-off-by: Jianyong Wu --- arch/arm64/mm/mmu.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index acfae9b41cc8..98ac09ae9588 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -63,6 +63,7 @@ static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused; static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused; static DEFINE_SPINLOCK(swapper_pgdir_lock); +static DEFINE_SPINLOCK(fixmap_lock); void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd) { @@ -329,6 +330,11 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } BUG_ON(p4d_bad(p4d)); + /* + * fixmap is global resource, thus it needs to be protected by a lock + * in case of race condition. + */ + spin_lock(&fixmap_lock); pudp = pud_set_fixmap_offset(p4dp, addr); do { pud_t old_pud = READ_ONCE(*pudp); @@ -359,6 +365,7 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } while (pudp++, addr = next, addr != end); pud_clear_fixmap(); + spin_unlock(&fixmap_lock); } static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys, -- 2.17.1