From patchwork Mon May 29 06:16:16 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hugh Dickins X-Patchwork-Id: 13258156 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 11262C77B7A for ; Mon, 29 May 2023 06:16:48 +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:MIME-Version:References:Message-ID: In-Reply-To:Subject:cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=H2QfV0VRbkJuzfh83dygo7ipwEsnd+24LMvPNrt+2KI=; b=0YJ3dAN/xH0m+e Lt1I9aAWZMvEi/RnxpFK6KOl2f0wPkWnb9d6nW7ZxkR/fVFN21D4AcSGLZ2L3I6lzqccrlM9KJyVx rDvTcBiasgtH6b2QHgjRuLtf/1GgrlAtkSQLsym2IrgMF1UjdVQHGl86XH+6VYivEarNoYpBiAdws +d6DFx+kLoA3q4LPN5sSAw0a7YRl3zsKQiYfKP3NB69Xz34paRwPsB8xKneuTOq0BoghSgVe9H07E Z5REB+eAinvEGyPkAUrg5adwsYG5NH1a8jYdiFY/g4HPyegTX/IqxFYOkjR86fx70hB757iT+ixcJ F9iwvySPOu82I4vl2RwQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1q3WB8-009Kzh-14; Mon, 29 May 2023 06:16:26 +0000 Received: from mail-yw1-x112e.google.com ([2607:f8b0:4864:20::112e]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1q3WB3-009KwZ-2o for linux-arm-kernel@lists.infradead.org; Mon, 29 May 2023 06:16:24 +0000 Received: by mail-yw1-x112e.google.com with SMTP id 00721157ae682-565e6beb7aaso19222027b3.2 for ; Sun, 28 May 2023 23:16:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1685340981; x=1687932981; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=xPq2eB/hW7ShnFytnKcTY7aukisfg/jLLLPKQ4lP3rM=; b=TyhMHkB8EAAdy+hUHa48C2vLWt0oIXv3HPWA7oGBtoKurezV9dmnaHp/Ug08+YXBMJ q7/doDqEaB13J8DWMDOsmxCRPRcN6V2SXOTsYe+dqJjrxA7f0LVq1fNiXr9IMn2dnMMI ESckYbJKgJgrbJ8T+uYkbBEglbSci8JLRkQ5xTjOVaaAsg2STz0pP4v2Ide+0MWDvyHe y1hUI8uDpAzlLTOdYFAa9G5upyPvxazDxgjqrZ/FkHni8ZrS3oyiM+Gr8t/oORl7+XNi bEMYjRBzoNKzLiTXOPBKXj7pF37UgxQaCI1yMdVBb74YQf5DcZFdirdn0N62WO3feJu6 qWEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685340981; x=1687932981; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=xPq2eB/hW7ShnFytnKcTY7aukisfg/jLLLPKQ4lP3rM=; b=ltKM/IaFoJZy6YrvMZiTpLXOqus9mweFfZRZfGlLbcR2/CijDkTQL6S3sl9QsMkFKy kUZuSglpYCb3NvaRYIXX81e4AvdVY1/AmCdjWf82b/fFT+I0g4E6HEAySDECzmJKyb/v Ii2IGddYzlx6gnl50hDLfYirj+ADwoo+7PBqhrmeJ06acJTl8jbtFCuOpEGLAM2a7sWY GVYyBcAqTrAMGYjuoZEq8t1T53l8Y2tYKGhEAre9eZ/L1zPhscfNAg/moY9kr1Wea7sf qWUISPNDWjRwqGZMFfChJuhWpAk5RDkQWT4En5Lg812/qlZ2BvG2YfeJd/OdGsiFQuGv WB0Q== X-Gm-Message-State: AC+VfDzUCwWI6phBjD6wdNM7iHErmY1RAmDoNkJZ7WOyyUyFPCj/FyK5 aWmmrVs31GyMBgqvdTAqxPkeAA== X-Google-Smtp-Source: ACHHUZ5ZacpUNHnx35XFkkfr+0IABaEA7Bz0HX1XL9bgqfNu7gBbTpGfMWgF9E5JOg8lgzwGl1APAA== X-Received: by 2002:a0d:f003:0:b0:565:a0c8:7e66 with SMTP id z3-20020a0df003000000b00565a0c87e66mr11630388ywe.0.1685340981021; Sun, 28 May 2023 23:16:21 -0700 (PDT) Received: from ripple.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id n5-20020a819c45000000b00545a081847fsm3407533ywa.15.2023.05.28.23.16.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 28 May 2023 23:16:20 -0700 (PDT) Date: Sun, 28 May 2023 23:16:16 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David S. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Jann Horn , linux-arm-kernel@lists.infradead.org, sparclinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 02/12] mm/pgtable: add PAE safety to __pte_offset_map() In-Reply-To: <35e983f5-7ed3-b310-d949-9ae8b130cdab@google.com> Message-ID: <923480d5-35ab-7cac-79d0-343d16e29318@google.com> References: <35e983f5-7ed3-b310-d949-9ae8b130cdab@google.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230528_231621_909833_C09CB8F0 X-CRM114-Status: GOOD ( 18.25 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org There is a faint risk that __pte_offset_map(), on a 32-bit architecture with a 64-bit pmd_t e.g. x86-32 with CONFIG_X86_PAE=y, would succeed on a pmdval assembled from a pmd_low and a pmd_high which never belonged together: their combination not pointing to a page table at all, perhaps not even a valid pfn. pmdp_get_lockless() is not enough to prevent that. Guard against that (on such configs) by local_irq_save() blocking TLB flush between present updates, as linux/pgtable.h suggests. It's only needed around the pmdp_get_lockless() in __pte_offset_map(): a race when __pte_offset_map_lock() repeats the pmdp_get_lockless() after getting the lock, would just send it back to __pte_offset_map() again. CONFIG_GUP_GET_PXX_LOW_HIGH is enabled when required by mips, sh and x86. It is not enabled by arm-32 CONFIG_ARM_LPAE: my understanding is that Will Deacon's 2020 enhancements to READ_ONCE() are sufficient for arm. It is not enabled by arc, but its pmd_t is 32-bit even when pte_t 64-bit. Limit the IRQ disablement to CONFIG_HIGHPTE? Perhaps, but would need a little more work, to retry if pmd_low good for page table, but pmd_high non-zero from THP (and that might be making x86-specific assumptions). Signed-off-by: Hugh Dickins --- mm/pgtable-generic.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index 674671835631..d28b63386cef 100644 --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -232,12 +232,32 @@ pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address, #endif #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ +#if defined(CONFIG_GUP_GET_PXX_LOW_HIGH) && \ + (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RCU)) +/* + * See the comment above ptep_get_lockless() in include/linux/pgtable.h: + * the barriers in pmdp_get_lockless() cannot guarantee that the value in + * pmd_high actually belongs with the value in pmd_low; but holding interrupts + * off blocks the TLB flush between present updates, which guarantees that a + * successful __pte_offset_map() points to a page from matched halves. + */ +#define config_might_irq_save(flags) local_irq_save(flags) +#define config_might_irq_restore(flags) local_irq_restore(flags) +#else +#define config_might_irq_save(flags) +#define config_might_irq_restore(flags) +#endif + pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp) { + unsigned long __maybe_unused flags; pmd_t pmdval; rcu_read_lock(); + config_might_irq_save(flags); pmdval = pmdp_get_lockless(pmd); + config_might_irq_restore(flags); + if (pmdvalp) *pmdvalp = pmdval; if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval)))