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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 772FDC282CE for ; Wed, 22 May 2019 19:21:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4A2912173C for ; Wed, 22 May 2019 19:21:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558552877; bh=YbWw5jCdlVSPKASk0Am85SMF0LzLvtSiYq/4581+xHE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=1vRsWL+MSigby2aDMiwzTj//xhpdoEWDRrIUxmyh1RnbyhoDL+Bn/SR+PcE2XW4kX 8rWKOooMtScJRqET0/Lc+NTo4a6dWoJ+qKLc0ccK6/6bbPqdPWnXf9f6SE6wYt5tuz CPxiV/Va4GW5KyMAhtWQNCzcQetvAaUaKD0VX5tM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729712AbfEVTVQ (ORCPT ); Wed, 22 May 2019 15:21:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:41606 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728615AbfEVTVQ (ORCPT ); Wed, 22 May 2019 15:21:16 -0400 Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 523F120879; Wed, 22 May 2019 19:21:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558552875; bh=YbWw5jCdlVSPKASk0Am85SMF0LzLvtSiYq/4581+xHE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=wlA5IMAkbdJJK84FwgfTk9vb9mKRpiUrE0gdmAYhRNeZdEZWLa1O+1TqMzYFFDkfR m8FRQRwg28nthhrzfBj+wuGjErUBKAjaQqkxYOpUwt4Yv2Q5F1PzzdjoWN+gmExmTD OETzWa9p/CSYA14EHx9WnsYDpghD4UP96mMh+maQ= Date: Wed, 22 May 2019 12:21:13 -0700 From: Andrew Morton To: Mike Rapoport Cc: Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sebastian Andrzej Siewior , Borislav Petkov Subject: Re: [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults Message-Id: <20190522122113.a2edc8aba32f0fad189bae21@linux-foundation.org> In-Reply-To: <1557844195-18882-1-git-send-email-rppt@linux.ibm.com> References: <1557844195-18882-1-git-send-email-rppt@linux.ibm.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 14 May 2019 17:29:55 +0300 Mike Rapoport wrote: > When get_user_pages*() is called with pages = NULL, the processing of > VM_FAULT_RETRY terminates early without actually retrying to fault-in all > the pages. > > If the pages in the requested range belong to a VMA that has userfaultfd > registered, handle_userfault() returns VM_FAULT_RETRY *after* user space > has populated the page, but for the gup pre-fault case there's no actual > retry and the caller will get no pages although they are present. > > This issue was uncovered when running post-copy memory restore in CRIU > after commit d9c9ce34ed5c ("x86/fpu: Fault-in user stack if > copy_fpstate_to_sigframe() fails"). > > After this change, the copying of FPU state to the sigframe switched from > copy_to_user() variants which caused a real page fault to get_user_pages() > with pages parameter set to NULL. You're saying that argument buf_fx in copy_fpstate_to_sigframe() is NULL? If so was that expected by the (now cc'ed) developers of d9c9ce34ed5c8923 ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails")? It seems rather odd. copy_fpregs_to_sigframe() doesn't look like it's expecting a NULL argument. Also, I wonder if copy_fpstate_to_sigframe() would be better using fault_in_pages_writeable() rather than get_user_pages_unlocked(). That seems like it operates at a more suitable level and I guess it will fix this issue also. > In post-copy mode of CRIU, the destination memory is managed with > userfaultfd and lack of the retry for pre-fault case in get_user_pages() > causes a crash of the restored process. > > Making the pre-fault behavior of get_user_pages() the same as the "normal" > one fixes the issue. Should this be backported into -stable trees? > Fixes: d9c9ce34ed5c ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails") > Signed-off-by: Mike Rapoport