From mboxrd@z Thu Jan 1 00:00:00 1970 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 B78BCC433F5 for ; Mon, 13 Dec 2021 06:57:55 +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:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:Cc:To:Subject:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=Omg6cBpP75CRrDQDpqrGZG0Enipvic3QJs6scIoNhl0=; b=OV9Z/NufgCHFuTJnq5pmqAumnB QeFs6WY0YHwGCWR1XhoGQJGi8CPHEBK/tNChb/1v9B6/naX+7PFIdy0oEGSP5g4GXPqCh5o3FwZra x8TlAKiS2ZT7s/ciDKzkQYE3W30Gz04/lPWQzqIGzX30L380mb/qZiAb+ByLV+lQdRQGp/5t6CgDT qW4sBS5q2tBSt0qriQdPvc5UALp64QdXefIw95EHs/TYOy+Rtns5p7PZ/NAMRAgYH976HrXThyMuI 1FAl/GK7L75WpdQU+UJKODwAXqmIwvUGG4hL/xpLmXZwG6kTbdcFTv4xzUpoGWuSn4EPDl2JLz1Cr yrEBdIWw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mwfG5-00803o-Ub; Mon, 13 Dec 2021 06:56:26 +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 1mwfG2-00802s-3D for linux-arm-kernel@lists.infradead.org; Mon, 13 Dec 2021 06:56:23 +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 28DD4106F; Sun, 12 Dec 2021 22:56:18 -0800 (PST) Received: from [10.163.67.80] (unknown [10.163.67.80]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 060C13F73B; Sun, 12 Dec 2021 22:56:14 -0800 (PST) Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping To: Jianyong Wu , catalin.marinas@arm.com, will@kernel.org, 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, nd@arm.com References: <20211210095432.51798-1-jianyong.wu@arm.com> From: Anshuman Khandual Message-ID: Date: Mon, 13 Dec 2021 12:26:13 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20211210095432.51798-1-jianyong.wu@arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211212_225622_247426_F0855DCF X-CRM114-Status: GOOD ( 18.68 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 12/10/21 3:24 PM, Jianyong Wu wrote: > 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, > As the race could only happen with memory hotplug being enabled, could not we wrap this around with CONFIG_MEMORY_HOTPLUG, just to narrow its scope possibly speed up other non-hotplug cases ? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel