From patchwork Fri Dec 10 09:54:32 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jianyong Wu X-Patchwork-Id: 12695581 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CA604C433EF for ; Fri, 10 Dec 2021 09:56:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:MIME-Version:List-Subscribe:List-Help: List-Post:List-Archive:List-Unsubscribe:List-Id:Message-Id:Date:Subject:Cc:To :From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References: List-Owner; bh=rvh3U3z/D1IYOPjWgSvZxnYFCKfJI6D9m1CWb+25lEs=; b=XNt5GbEEd4wjTu gMWqJUUb8XRCajAxjH92G+yg9OdFpg6pCPKZp3VemSuLdA7dKN5Kq25cx9RDfOzmfo2zI8nn57sS7 SuRcGRaN92GC6X4s6fsGdv0wcQkLMyXI0XVXTxE/SdPJH/l1HSTpZiGFYdSaQBRKuaY5iHFyq7iGX MQym57Icfz4UkCxPbJnX3OmCY8iXkghxwtuCnysTnXNI00NAp7TZIjEiTwdTUiDT/uuVzj6DoWEBj 1rNfN/o6SdHcoQGuHHh0n4G4FwzRpCCZdC8KlAlR/YNd7e/cCKsazj/CZ9Ro7see8G7VK53rv3NJ3 fpcUsgaTOTDLNtW8SfYQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvcc7-001QRI-Fd; Fri, 10 Dec 2021 09:54:51 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvcc3-001QPi-II for linux-arm-kernel@lists.infradead.org; Fri, 10 Dec 2021 09:54:49 +0000 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211210_015447_692955_D0245A3A X-CRM114-Status: UNSURE ( 7.46 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 Reviewed-by: Catalin Marinas Reviewed-by: Anshuman Khandual --- 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,