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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E275BC3A59D for ; Mon, 24 Oct 2022 04:35:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229906AbiJXEfK (ORCPT ); Mon, 24 Oct 2022 00:35:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41576 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229613AbiJXEfF (ORCPT ); Mon, 24 Oct 2022 00:35:05 -0400 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B7FC1248CD for ; Sun, 23 Oct 2022 21:35:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1666586102; x=1698122102; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=AZBlPxqq4LjioAqMcl77X4b+mE9LrGUprIKCn0OV7KE=; b=DensI+mXVOXgkGaL8Fr27f02H9TqLDJS1Z1SpSFfV6CtykpHCB2Ma/v8 LxbImvZbjwBiEZtB3k9Ew47DRBd7PjnqeOAoK7vSzm1jnqIE0LCYFyXtp zhmWMwdi58DD7x8GRDg+sx3lTknpWxKJDgkOHtEo2FeY6yCqHJ8zVZw/t ZQWEOAQO0g7BCgYv+XqnPxH3cA3ORADvNToRbRdJx5FG2Nj4iPIeRO1VE L2pbL+3ST7u0uGlQCFUe+cPZy8Mx5d3+OEdtrgn4Xm+z5FN5IBuhrQ5XI GmRjQHuKeOf6ehMUKeRpspS18Jhde0C0IMcQV6a7RxI/HfKkyskVk/LFJ g==; X-IronPort-AV: E=McAfee;i="6500,9779,10509"; a="290638532" X-IronPort-AV: E=Sophos;i="5.95,207,1661842800"; d="scan'208";a="290638532" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2022 21:35:01 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10509"; a="736273355" X-IronPort-AV: E=Sophos;i="5.95,207,1661842800"; d="scan'208";a="736273355" Received: from iweiny-mobl.amr.corp.intel.com (HELO localhost) ([10.252.130.95]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2022 21:35:01 -0700 From: ira.weiny@intel.com To: Andrew Morton Cc: Ira Weiny , Matthew Wilcox , Andrea Arcangeli , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm/userfaultfd: Replace kmap/kmap_atomic() with kmap_local_page() Date: Sun, 23 Oct 2022 21:34:52 -0700 Message-Id: <20221024043452.1491677-1-ira.weiny@intel.com> X-Mailer: git-send-email 2.37.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ira Weiny kmap() and kmap_atomic() are being deprecated in favor of kmap_local_page() which is appropriate for any thread local context.[1] A recent locking bug report with userfaultfd showed that the conversion of these kmap_atomic()'s required care with regard to the prevention of deadlock.[2] Complete kmap conversion in userfaultfd by replacing the kmap() and kmap_atomic() calls with kmap_local_page(). When replacing the kmap_atomic() call ensure page faults continue to be disabled to support the correct fall back behavior and add a comment to inform future souls of the requirement. [1] https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/ [2] https://lore.kernel.org/all/Y1Mh2S7fUGQ%2FiKFR@iweiny-desk3/ Cc: Matthew Wilcox Cc: Andrew Morton Cc: Andrea Arcangeli Signed-off-by: Ira Weiny --- mm/userfaultfd.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index e24e8a47ce8a..c5db06f4d28d 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -157,11 +157,18 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm, if (!page) goto out; - page_kaddr = kmap_atomic(page); + page_kaddr = kmap_local_page(page); + /* + * The mmap_lock is held here. Disable page faults to + * prevent deadlock should copy_from_user() fault. The + * copy will be retried outside the mmap_lock. + */ + pagefault_disable(); ret = copy_from_user(page_kaddr, (const void __user *) src_addr, PAGE_SIZE); - kunmap_atomic(page_kaddr); + pagefault_enable(); + kunmap_local(page_kaddr); /* fallback to copy_from_user outside mmap_lock */ if (unlikely(ret)) { @@ -646,11 +653,11 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm, mmap_read_unlock(dst_mm); BUG_ON(!page); - page_kaddr = kmap(page); + page_kaddr = kmap_local_page(page); err = copy_from_user(page_kaddr, (const void __user *) src_addr, PAGE_SIZE); - kunmap(page); + kunmap_local(page_kaddr); if (unlikely(err)) { err = -EFAULT; goto out; -- 2.37.2