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 AB4DDC43334 for ; Wed, 20 Jul 2022 09:43:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231982AbiGTJnG (ORCPT ); Wed, 20 Jul 2022 05:43:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43678 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231546AbiGTJnC (ORCPT ); Wed, 20 Jul 2022 05:43:02 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4F7916391A for ; Wed, 20 Jul 2022 02:43:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1658310179; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6RKfphNn3mPOW1MXkGNfh4n+QtAmR71ynMhMeD/fO8E=; b=fOcmHKZyIY5ZrJMDar458RiargpP2dxnDbnrf7o7RZfeXyhkVyfC0uECKsT6Bap2UE2I+8 2eCGNuD3PEFyW7rBVLghtBeIEYZjbhAzHGwMWAo4Grz680PbHjCrtzLJH16z7CPm5EDVOK 7hIDK+7XRwDWGUvYlzm6fA3cbnvteeo= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-612-2ilFvp8NP9-A6YwBC5l8HQ-1; Wed, 20 Jul 2022 05:42:58 -0400 X-MC-Unique: 2ilFvp8NP9-A6YwBC5l8HQ-1 Received: by mail-wr1-f70.google.com with SMTP id l11-20020adfbd8b000000b0021d754b84c5so3041210wrh.17 for ; Wed, 20 Jul 2022 02:42:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:organization:in-reply-to :content-transfer-encoding; bh=6RKfphNn3mPOW1MXkGNfh4n+QtAmR71ynMhMeD/fO8E=; b=uMmIfMbSiD/St+Nx9graEXROZf1HkPte/FdXCt8cdc1Hqa/YrtNwrOTZkcbZUIAg6F XJoQHvsX31UUi7P1/thvtiAT5HmwuL/hrXdPRNst3QJqAZSnJzyWwQkm2aXlrZu7TeK1 ajnR6wlP0WNT3sxtbw1dEGBDMPVPOxZh0r7ADjZ9mYr509/D9u+RQwvIFioHAIgmKzb4 aJ0zfdfky7cQS8BarPfN+8tl24oPkp1a94x//Q96XoRzZWFA38aWD34/UJsKcIRBCQko IumlOQtzRMe1IMwIiESfnmxJqSUbUD1MyTwOE3SFWPNWVeMghMl0CIWPis+6f+4N5SAP OpQw== X-Gm-Message-State: AJIora+9yRQfro/IyEn9epnwoYrgjmXBrXvIAyG3osFr1pXbn4xE2kA+ EVTIU0N36P1Lpb2oMoPep7dmwAJTf4Wu7b8xOiXd9Lw8jBSo1nfcnzI8DkaZ/q3kOstgUH3mS/a mhQ07hLoxLicOVhHiTgBK9ufD X-Received: by 2002:a05:6000:1a88:b0:21d:aa97:cb16 with SMTP id f8-20020a0560001a8800b0021daa97cb16mr30480722wry.97.1658310176899; Wed, 20 Jul 2022 02:42:56 -0700 (PDT) X-Google-Smtp-Source: AGRyM1vLkuZu1Isp50EKcsrNnkjav5J73V5/aUvap3rND17xDst4/UY0s1U6Yu8aeSvpX5+PIIk6cA== X-Received: by 2002:a05:6000:1a88:b0:21d:aa97:cb16 with SMTP id f8-20020a0560001a8800b0021daa97cb16mr30480707wry.97.1658310176663; Wed, 20 Jul 2022 02:42:56 -0700 (PDT) Received: from ?IPV6:2003:cb:c706:e00:8d96:5dba:6bc4:6e89? (p200300cbc7060e008d965dba6bc46e89.dip0.t-ipconnect.de. [2003:cb:c706:e00:8d96:5dba:6bc4:6e89]) by smtp.gmail.com with ESMTPSA id h12-20020a05600c28cc00b003a325bd8517sm2190898wmd.5.2022.07.20.02.42.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Jul 2022 02:42:56 -0700 (PDT) Message-ID: <09d84297-65d5-a3df-fdc0-a7168cdb0798@redhat.com> Date: Wed, 20 Jul 2022 11:42:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [RFC PATCH 01/14] userfaultfd: set dirty and young on writeprotect Content-Language: en-US To: Nadav Amit , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Mike Rapoport , Axel Rasmussen , Nadav Amit , Andrea Arcangeli , Andrew Cooper , Andy Lutomirski , Dave Hansen , Peter Xu , Peter Zijlstra , Thomas Gleixner , Will Deacon , Yu Zhao , Nick Piggin References: <20220718120212.3180-1-namit@vmware.com> <20220718120212.3180-2-namit@vmware.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220718120212.3180-2-namit@vmware.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18.07.22 14:01, Nadav Amit wrote: > From: Nadav Amit > > When userfaultfd makes a PTE writable, it can now change the PTE > directly, in some cases, without going triggering a page-fault first. > Yet, doing so might leave the PTE that was write-unprotected as old and > clean. At least on x86, this would cause a >500 cycles overhead when the > PTE is first accessed. > > Use MM_CP_WILL_NEED to set the PTE as young and dirty when userfaultfd > gets a hint that the page is likely to be used. Avoid changing the PTE > to young and dirty in other cases to avoid excessive writeback and > messing with the page reclamation logic. > > Cc: Andrea Arcangeli > Cc: Andrew Cooper > Cc: Andrew Morton > Cc: Andy Lutomirski > Cc: Dave Hansen > Cc: David Hildenbrand > Cc: Peter Xu > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: Will Deacon > Cc: Yu Zhao > Cc: Nick Piggin > --- > include/linux/mm.h | 2 ++ > mm/mprotect.c | 9 ++++++++- > mm/userfaultfd.c | 8 ++++++-- > 3 files changed, 16 insertions(+), 3 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 9cc02a7e503b..4afd75ce5875 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1988,6 +1988,8 @@ extern unsigned long move_page_tables(struct vm_area_struct *vma, > /* Whether this change is for write protecting */ > #define MM_CP_UFFD_WP (1UL << 2) /* do wp */ > #define MM_CP_UFFD_WP_RESOLVE (1UL << 3) /* Resolve wp */ > +/* Whether to try to mark entries as dirty as they are to be written */ > +#define MM_CP_WILL_NEED (1UL << 4) > #define MM_CP_UFFD_WP_ALL (MM_CP_UFFD_WP | \ > MM_CP_UFFD_WP_RESOLVE) > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 996a97e213ad..34c2dfb68c42 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -82,6 +82,7 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, > bool prot_numa = cp_flags & MM_CP_PROT_NUMA; > bool uffd_wp = cp_flags & MM_CP_UFFD_WP; > bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; > + bool will_need = cp_flags & MM_CP_WILL_NEED; > > tlb_change_page_size(tlb, PAGE_SIZE); > > @@ -172,6 +173,9 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, > ptent = pte_clear_uffd_wp(ptent); > } > > + if (will_need) > + ptent = pte_mkyoung(ptent); > + > /* > * In some writable, shared mappings, we might want > * to catch actual write access -- see > @@ -187,8 +191,11 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, > */ > if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && > !pte_write(ptent) && Why would we want to check if we can set something writable if it already *is* writable? That doesn't make sense to me. > - can_change_pte_writable(vma, addr, ptent)) > + can_change_pte_writable(vma, addr, ptent)) { > ptent = pte_mkwrite(ptent); > + if (will_need) > + ptent = pte_mkdirty(ptent); > + } -- Thanks, David / dhildenb