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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id CFEC9C64ED6 for ; Wed, 1 Mar 2023 15:19:41 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0F3A66B0071; Wed, 1 Mar 2023 10:19:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 07D496B0072; Wed, 1 Mar 2023 10:19:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E60066B0073; Wed, 1 Mar 2023 10:19:40 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id D43AF6B0071 for ; Wed, 1 Mar 2023 10:19:40 -0500 (EST) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id A1EC8C0ACB for ; Wed, 1 Mar 2023 15:19:40 +0000 (UTC) X-FDA: 80520688920.15.73B59AF Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf17.hostedemail.com (Postfix) with ESMTP id A92DB4001F for ; Wed, 1 Mar 2023 15:19:36 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=VuIfleq5; spf=pass (imf17.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1677683977; a=rsa-sha256; cv=none; b=C54RImYCTTndXNtOAhHvh3pUtMoyzrJ7I395/fA7QskFSlNauV5ngXoodMn1n4E8Nr/JhT +JVHk+5iV47Up446P7gAKyZ42qz1Eo+CFzjwYd9cmuPACbryBQRwmQzkz63wh0gXSLX5qY GnZOz21TGUKV5vm7+Ut503uzrnOKySc= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=VuIfleq5; spf=pass (imf17.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1677683977; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Z+pi+Q3n6FAc/3Vit9mlFi0cKydtod+1ggFmBEFVzpQ=; b=u9FVVfQ2Uj2PnZOJpvVQNVrw91xNTVMdwZiOt8QNdt0ht9YHBT1KCrMeio/utO6+lusHLB uOMI3OfChOYJ+tpbHJo8GCbdaKFtjavJdWdAvv2tLdvsxOkKFSn8ZdgDDtFDuWHPazgZu/ +jWqsP8QiuD7JWlGDIQYad59i9CkOMs= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1677683976; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Z+pi+Q3n6FAc/3Vit9mlFi0cKydtod+1ggFmBEFVzpQ=; b=VuIfleq5baNgRuteMBPFh5MFPLsRhDzMJ9DApomI05gFB4xiW20idUb6Xjqk7NEKa6DT6D XrV4CIDOKBxTUR78QSQ3kw9zHL48Q2Qw8I6+zW7Q1BnYNl1fa4xpcuJBbxVUNw+6JvdAqI gUNil/LQRB4XFIQeNeVN/FSVTtJtWio= Received: from mail-qk1-f198.google.com (mail-qk1-f198.google.com [209.85.222.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-80-8v-FwwWPPrqsjrxi7b1Y-A-1; Wed, 01 Mar 2023 10:19:34 -0500 X-MC-Unique: 8v-FwwWPPrqsjrxi7b1Y-A-1 Received: by mail-qk1-f198.google.com with SMTP id y1-20020a05620a09c100b0070630ecfd9bso8205317qky.20 for ; Wed, 01 Mar 2023 07:19:34 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1677683974; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Z+pi+Q3n6FAc/3Vit9mlFi0cKydtod+1ggFmBEFVzpQ=; b=Q1P8PaKT/nYEVenspfqoTQvek6L5KVfQoNQuw7RqI8jvQ7yqG58zGKXhOtiMkvECjI pSwmkwjVPKa71SKrOn5rQXTxlXURoFppmd3Y+TI5l253H8lJMT1BM4lWoPA6PojPKUUq 0UdCB44Ij47q/CAnIqqSqB0C5Efoj4HG9pUz2s2IY9pBEMounyJSUSUKvhc8yqiDTItJ TvoxrgTsvKF9hy7x3oyJJ65xGmCIHPg9v/CTSI1JNKmT/oz7iXjOfC427kkx7AWz7wWL E1RHK8jHIvQp6jqSdOze937dqk8EKRPKErDL3sI1y4I2yhOzKvsVBPaXbC4/OMvF5tdf aKyQ== X-Gm-Message-State: AO0yUKVxy5FZt3Ptm0Bjx/6cBm2QNbtucZtMCKoj1PFnFcGDUnz9KBnq AlyfBYujdNLdxvs0DVt+NcElkXfEgTdGx/8w1anrH8fsO9HqbiuiOWr6I0LLHaG/5DvxKwK79Ia e2bvYbowx1ZA= X-Received: by 2002:a0c:9c0e:0:b0:56e:89b9:9a92 with SMTP id v14-20020a0c9c0e000000b0056e89b99a92mr12284249qve.0.1677683974091; Wed, 01 Mar 2023 07:19:34 -0800 (PST) X-Google-Smtp-Source: AK7set9OWJnH61ne7rRBbSI97/TEcVm5h0Ds8qUHxmuqzkd3WaHEYcHLo+QzJXxkDpHeSBu4A2GKIA== X-Received: by 2002:a0c:9c0e:0:b0:56e:89b9:9a92 with SMTP id v14-20020a0c9c0e000000b0056e89b99a92mr12284208qve.0.1677683973761; Wed, 01 Mar 2023 07:19:33 -0800 (PST) Received: from x1n (bras-base-aurron9127w-grc-56-70-30-145-63.dsl.bell.ca. [70.30.145.63]) by smtp.gmail.com with ESMTPSA id p13-20020a05620a15ed00b006fed58fc1a3sm8940339qkm.119.2023.03.01.07.19.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Mar 2023 07:19:32 -0800 (PST) Date: Wed, 1 Mar 2023 10:19:31 -0500 From: Peter Xu To: Muhammad Usama Anjum Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Mike Rapoport , Axel Rasmussen , Nadav Amit , David Hildenbrand , "kernel@collabora.com" Subject: Re: [PATCH v2] mm/uffd: UFFD_FEATURE_WP_UNPOPULATED Message-ID: References: <20230227230044.1596744-1-peterx@redhat.com> <640319be-ddb6-d74f-b731-eee5ceab3d01@collabora.com> MIME-Version: 1.0 In-Reply-To: <640319be-ddb6-d74f-b731-eee5ceab3d01@collabora.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Queue-Id: A92DB4001F X-Rspamd-Server: rspam01 X-Stat-Signature: 7ho6zpizotkqy4wfi1xjmmmfpkh6uprx X-HE-Tag: 1677683976-835883 X-HE-Meta: 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 RVC9rfe8 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 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: On Wed, Mar 01, 2023 at 12:55:51PM +0500, Muhammad Usama Anjum wrote: > Hi Peter, Hi, Muhammad, > While using WP_UNPOPULATED, we get stuck if newly allocated memory is read > without initialization. This can be reproduced by either of the following > statements: > printf("%c", buffer[0]); > buffer[0]++; > > This bug has start to appear on this patch. How are you handling reading > newly allocated memory when WP_UNPOPULATED is defined? Yes it's a bug, thanks for the reproducer. You're right I missed a trivial but important detail. Could you try apply below on top? ---8<--- diff --git a/mm/memory.c b/mm/memory.c index 46934133bd0b..2f4b3892948b 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4062,7 +4062,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) vma->vm_page_prot)); vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); - if (!pte_none(*vmf->pte)) { + if (vmf_pte_changed(vmf)) { update_mmu_tlb(vma, vmf->address, vmf->pte); goto unlock; } ---8<--- I can send a new version after you confirmed it at least works on your side. I'll also add some more test to cover that in the next version. The current smoke test within this patch is really light; I somehow rely on you on this patch on the testing side, and thanks for that. > Running my pagemap_ioctl selftest as benchmark in a VM: > without zeropage / wp_unpopulated (decide from pte_none() if page is dirty > or not, buggy and wrong implementation, just for reference) > 26.608 seconds > with zeropage > 39.203 seconds > with wp_unpopulated > 62.907 seconds > > 136% worse performance overall > 60% worse performance of unpopulated than zeropage Yes this is unfortunate, because we're protecting more things than before when with WP_ZEROPAGE / WP_UNPOPULATED but that's what it is for (when we want to make sure that accuracy on the holes). I didn't look closer to your whole test suite yet, but my pure test on protection above should mean that it's still much better for such a use case than either (1) pre-read or (2) MADV_POPULATE_READ. Again, I hope the performance result is not a concern to you. If it is, please let us know. Thanks, -- Peter Xu