From patchwork Fri Apr 29 13:35:43 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qi Zheng X-Patchwork-Id: 12832014 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E388C433F5 for ; Fri, 29 Apr 2022 13:37:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 38EA26B0074; Fri, 29 Apr 2022 09:37:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 33D8B6B007E; Fri, 29 Apr 2022 09:37:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 205856B0080; Fri, 29 Apr 2022 09:37:11 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id 139116B0074 for ; Fri, 29 Apr 2022 09:37:11 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id DED3D265EA for ; Fri, 29 Apr 2022 13:37:10 +0000 (UTC) X-FDA: 79410017820.10.5B3C809 Received: from mail-pl1-f177.google.com (mail-pl1-f177.google.com [209.85.214.177]) by imf02.hostedemail.com (Postfix) with ESMTP id BBBB18004A for ; Fri, 29 Apr 2022 13:37:06 +0000 (UTC) Received: by mail-pl1-f177.google.com with SMTP id p6so7151017plf.9 for ; Fri, 29 Apr 2022 06:37:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=DGl50d69T/46DVPYmj2DL1x7ncKmmZ54JyK/lw6nQrc=; b=ARePECzUIuI/o7LaJ6U30K3W4hzXRsvLwyPDJjZN5Ir39F24/V1LJiWa1QSu1EMnH5 A1GdbC0XtJEshbkbFIKnlj/USWQUZJ1ZbMvKe6cExn1vdQNp2EvKrmONYlgc4UfzDqDN NPrE/d77mWvSMe8t+Pj6PUpwZJtO1lp6YSqboATYrrZ7UX43LUsVHKLtdYbl0QShre5S KTKyDJkzYVYEsW858cbU/F6b9nm45sIAiNbvtYGtEbXr8MjkUHvyh6vh9G95S67sc/Qd 5bayvVPY/1MQqIcZ8qKIQkAnNN6I1m7O69zc83csx5Wy9gJ5vcWF0bOjLvSmoOPA1ADx MHpQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=DGl50d69T/46DVPYmj2DL1x7ncKmmZ54JyK/lw6nQrc=; b=K6ptEpY1aKyii38H9ixjBA+uccSCiiupl4l9UnvdMi0awgai4twMc3ms5XVKEOIFm3 rL+JetBvTF2h6vuv1uA8bePPNzG+W/JVyzuEm9ZCM5Z4O3XvJfI6TRJk1UwmmHcSZ2FA E1HzO6UJ4/TardmzK+3c6bIkGgy/yL3BBQWxFnJgD9dXclCnHzkOUisKBEXHlYIZHG8K ANr/lmSAjYZpNUbKHaFjkruTG9cWtdSbo4VxI5XZf2QgguuxDUToQdmM+29kyh/CajBN kFfN75OL5rlUY4ZywYOHG0g9tgd7gCrcI4pXG8t/qGjXOG7MYzE37lYskyoFSjGiK0yQ gz1g== X-Gm-Message-State: AOAM5330PG0TJRd0UBnZj+GiCZioeh1+QW9KvwS1+Ph0t24h6Id73f71 84iR+UPi5TJEVIkhR9EUo4u+jg== X-Google-Smtp-Source: ABdhPJwkDEFr/eSiIXsECiLskFgBvhXhvx+Ht6goriTOJRM12m+x++WpdKjE8bfOm4QcHnGGrKiSMQ== X-Received: by 2002:a17:90b:380e:b0:1da:2943:b975 with SMTP id mq14-20020a17090b380e00b001da2943b975mr4006350pjb.42.1651239429455; Fri, 29 Apr 2022 06:37:09 -0700 (PDT) Received: from localhost.localdomain ([139.177.225.240]) by smtp.gmail.com with ESMTPSA id m8-20020a17090a414800b001d81a30c437sm10681977pjg.50.2022.04.29.06.37.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 Apr 2022 06:37:08 -0700 (PDT) From: Qi Zheng To: akpm@linux-foundation.org, tglx@linutronix.de, kirill.shutemov@linux.intel.com, mika.penttila@nextfour.com, david@redhat.com, jgg@nvidia.com, tj@kernel.org, dennis@kernel.org, ming.lei@redhat.com Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, songmuchun@bytedance.com, zhouchengming@bytedance.com, Qi Zheng Subject: [RFC PATCH 09/18] pte_ref: add pte_tryget() and {__,}pte_put() helper Date: Fri, 29 Apr 2022 21:35:43 +0800 Message-Id: <20220429133552.33768-10-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) In-Reply-To: <20220429133552.33768-1-zhengqi.arch@bytedance.com> References: <20220429133552.33768-1-zhengqi.arch@bytedance.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: BBBB18004A X-Stat-Signature: 5yw8y8wmr338qxqipjctr7cg7swxgt6j Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=ARePECzU; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf02.hostedemail.com: domain of zhengqi.arch@bytedance.com designates 209.85.214.177 as permitted sender) smtp.mailfrom=zhengqi.arch@bytedance.com X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1651239426-342439 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The user PTE page table page may be freed when the last percpu_ref is dropped. So we need to try to get its percpu_ref before accessing the PTE page to prevent it form being freed during the access process. This patch adds pte_tryget() and {__,}pte_put() to help us to get and put the percpu_ref of user PTE page table pages. Signed-off-by: Qi Zheng --- include/linux/pte_ref.h | 23 ++++++++++++++++ mm/pte_ref.c | 58 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 81 insertions(+) diff --git a/include/linux/pte_ref.h b/include/linux/pte_ref.h index d3963a151ca5..bfe620038699 100644 --- a/include/linux/pte_ref.h +++ b/include/linux/pte_ref.h @@ -12,6 +12,10 @@ bool pte_ref_init(pgtable_t pte); void pte_ref_free(pgtable_t pte); +void free_user_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr); +bool pte_tryget(struct mm_struct *mm, pmd_t *pmd, unsigned long addr); +void __pte_put(pgtable_t page); +void pte_put(pte_t *ptep); #else /* !CONFIG_FREE_USER_PTE */ @@ -24,6 +28,25 @@ static inline void pte_ref_free(pgtable_t pte) { } +static inline void free_user_pte(struct mm_struct *mm, pmd_t *pmd, + unsigned long addr) +{ +} + +static inline bool pte_tryget(struct mm_struct *mm, pmd_t *pmd, + unsigned long addr) +{ + return true; +} + +static inline void __pte_put(pgtable_t page) +{ +} + +static inline void pte_put(pte_t *ptep) +{ +} + #endif /* CONFIG_FREE_USER_PTE */ #endif /* _LINUX_PTE_REF_H */ diff --git a/mm/pte_ref.c b/mm/pte_ref.c index 52e31be00de4..5b382445561e 100644 --- a/mm/pte_ref.c +++ b/mm/pte_ref.c @@ -44,4 +44,62 @@ void pte_ref_free(pgtable_t pte) kfree(ref); } +void free_user_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr) {} + +/* + * pte_tryget - try to get the pte_ref of the user PTE page table page + * @mm: pointer the target address space + * @pmd: pointer to a PMD. + * @addr: virtual address associated with pmd. + * + * Return: true if getting the pte_ref succeeded. And false otherwise. + * + * Before accessing the user PTE page table, we need to hold a refcount to + * protect against the concurrent release of the PTE page table. + * But we will fail in the following case: + * - The content mapped in @pmd is not a PTE page + * - The pte_ref is zero, it may be reclaimed + */ +bool pte_tryget(struct mm_struct *mm, pmd_t *pmd, unsigned long addr) +{ + bool retval = true; + pmd_t pmdval; + pgtable_t pte; + + rcu_read_lock(); + pmdval = READ_ONCE(*pmd); + pte = pmd_pgtable(pmdval); + if (unlikely(pmd_none(pmdval) || pmd_leaf(pmdval))) { + retval = false; + } else if (!percpu_ref_tryget(pte->pte_ref)) { + rcu_read_unlock(); + /* + * Also do free_user_pte() here to prevent missed reclaim due + * to race condition. + */ + free_user_pte(mm, pmd, addr & PMD_MASK); + return false; + } + rcu_read_unlock(); + + return retval; +} + +void __pte_put(pgtable_t page) +{ + percpu_ref_put(page->pte_ref); +} + +void pte_put(pte_t *ptep) +{ + pgtable_t page; + + if (pte_huge(*ptep)) + return; + + page = pte_to_page(ptep); + __pte_put(page); +} +EXPORT_SYMBOL(pte_put); + #endif /* CONFIG_FREE_USER_PTE */