From patchwork Tue Aug 1 12:48:37 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13336667 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 A36BFC001E0 for ; Tue, 1 Aug 2023 12:49:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232662AbjHAMtu (ORCPT ); Tue, 1 Aug 2023 08:49:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47194 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232480AbjHAMtp (ORCPT ); Tue, 1 Aug 2023 08:49:45 -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 ESMTPS id E6BFD1FEE for ; Tue, 1 Aug 2023 05:48:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690894138; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PelEjOaWZH6A1jlfDs5yVYOsc8ih/vy8IfMPFWkWCRI=; b=TMtnSy9hmbUPVkoHHYgfVJG6YBekdOqlG1/gKMQD5/9CgTmh2nNfDPEaXiGpqvxXo16M9/ l99lJGLlU1bS6zQ4i/4sy1tlt6dlivuaA+cRW6ahVo8RLD64hq2Yejqs0GG78XNxrg/2uZ 3aGbkW2CRyZzG490MvSH77C09LTc7wQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-450-sCg6i6arPcC_qRSyqhkAOQ-1; Tue, 01 Aug 2023 08:48:55 -0400 X-MC-Unique: sCg6i6arPcC_qRSyqhkAOQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5A5D6104458A; Tue, 1 Aug 2023 12:48:54 +0000 (UTC) Received: from t14s.fritz.box (unknown [10.39.193.232]) by smtp.corp.redhat.com (Postfix) with ESMTP id E8606C585A0; Tue, 1 Aug 2023 12:48:49 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, David Hildenbrand , Andrew Morton , Linus Torvalds , liubo , Peter Xu , Matthew Wilcox , Hugh Dickins , Jason Gunthorpe , John Hubbard , Mel Gorman , Shuah Khan , Paolo Bonzini , stable@vger.kernel.org Subject: [PATCH v2 1/8] mm/gup: reintroduce FOLL_NUMA as FOLL_HONOR_NUMA_FAULT Date: Tue, 1 Aug 2023 14:48:37 +0200 Message-ID: <20230801124844.278698-2-david@redhat.com> In-Reply-To: <20230801124844.278698-1-david@redhat.com> References: <20230801124844.278698-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Unfortunately commit 474098edac26 ("mm/gup: replace FOLL_NUMA by gup_can_follow_protnone()") missed that follow_page() and follow_trans_huge_pmd() never implicitly set FOLL_NUMA because they really don't want to fail on PROT_NONE-mapped pages -- either due to NUMA hinting or due to inaccessible (PROT_NONE) VMAs. As spelled out in commit 0b9d705297b2 ("mm: numa: Support NUMA hinting page faults from gup/gup_fast"): "Other follow_page callers like KSM should not use FOLL_NUMA, or they would fail to get the pages if they use follow_page instead of get_user_pages." liubo reported [1] that smaps_rollup results are imprecise, because they miss accounting of pages that are mapped PROT_NONE. Further, it's easy to reproduce that KSM no longer works on inaccessible VMAs on x86-64, because pte_protnone()/pmd_protnone() also indictaes "true" in inaccessible VMAs, and follow_page() refuses to return such pages right now. As KVM really depends on these NUMA hinting faults, removing the pte_protnone()/pmd_protnone() handling in GUP code completely is not really an option. To fix the issues at hand, let's revive FOLL_NUMA as FOLL_HONOR_NUMA_FAULT to restore the original behavior for now and add better comments. Set FOLL_HONOR_NUMA_FAULT independent of FOLL_FORCE in is_valid_gup_args(), to add that flag for all external GUP users. Note that there are three GUP-internal __get_user_pages() users that don't end up calling is_valid_gup_args() and consequently won't get FOLL_HONOR_NUMA_FAULT set. 1) get_dump_page(): we really don't want to handle NUMA hinting faults. It specifies FOLL_FORCE and wouldn't have honored NUMA hinting faults already. 2) populate_vma_page_range(): we really don't want to handle NUMA hinting faults. It specifies FOLL_FORCE on accessible VMAs, so it wouldn't have honored NUMA hinting faults already. 3) faultin_vma_page_range(): we similarly don't want to handle NUMA hinting faults. To make the combination of FOLL_FORCE and FOLL_HONOR_NUMA_FAULT work in inaccessible VMAs properly, we have to perform VMA accessibility checks in gup_can_follow_protnone(). As GUP-fast should reject such pages either way in pte_access_permitted()/pmd_access_permitted() -- for example on x86-64 and arm64 that both implement pte_protnone() -- let's just always fallback to ordinary GUP when stumbling over pte_protnone()/pmd_protnone(). As Linus notes [2], honoring NUMA faults might only make sense for selected GUP users. So we should really see if we can instead let relevant GUP callers specify it manually, and not trigger NUMA hinting faults from GUP as default. Prepare for that by making FOLL_HONOR_NUMA_FAULT an external GUP flag and adding appropriate documenation. [1] https://lore.kernel.org/r/20230726073409.631838-1-liubo254@huawei.com [2] https://lore.kernel.org/r/CAHk-=wgRiP_9X0rRdZKT8nhemZGNateMtb366t37d8-x7VRs=g@mail.gmail.com Reported-by: liubo Closes: https://lore.kernel.org/r/20230726073409.631838-1-liubo254@huawei.com Reported-by: Peter Xu Closes: https://lore.kernel.org/all/ZMKJjDaqZ7FW0jfe@x1n/ Fixes: 474098edac26 ("mm/gup: replace FOLL_NUMA by gup_can_follow_protnone()") Cc: Signed-off-by: David Hildenbrand Acked-by: Peter Xu Acked-by: Mel Gorman --- include/linux/mm.h | 21 +++++++++++++++------ include/linux/mm_types.h | 9 +++++++++ mm/gup.c | 29 +++++++++++++++++++++++------ mm/huge_memory.c | 2 +- 4 files changed, 48 insertions(+), 13 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 2fbc6c631764..165830a95641 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3455,15 +3455,24 @@ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags) * Indicates whether GUP can follow a PROT_NONE mapped page, or whether * a (NUMA hinting) fault is required. */ -static inline bool gup_can_follow_protnone(unsigned int flags) +static inline bool gup_can_follow_protnone(struct vm_area_struct *vma, + unsigned int flags) { /* - * FOLL_FORCE has to be able to make progress even if the VMA is - * inaccessible. Further, FOLL_FORCE access usually does not represent - * application behaviour and we should avoid triggering NUMA hinting - * faults. + * If callers don't want to honor NUMA hinting faults, no need to + * determine if we would actually have to trigger a NUMA hinting fault. */ - return flags & FOLL_FORCE; + if (!(flags & FOLL_HONOR_NUMA_FAULT)) + return true; + + /* + * NUMA hinting faults don't apply in inaccessible (PROT_NONE) VMAs. + * + * Requiring a fault here even for inaccessible VMAs would mean that + * FOLL_FORCE cannot make any progress, because handle_mm_fault() + * refuses to process NUMA hinting faults in inaccessible VMAs. + */ + return !vma_is_accessible(vma); } typedef int (*pte_fn_t)(pte_t *pte, unsigned long addr, void *data); diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index da538ff68953..18c8c3d793b0 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1296,6 +1296,15 @@ enum { FOLL_PCI_P2PDMA = 1 << 10, /* allow interrupts from generic signals */ FOLL_INTERRUPTIBLE = 1 << 11, + /* + * Always honor (trigger) NUMA hinting faults. + * + * FOLL_WRITE implicitly honors NUMA hinting faults because a + * PROT_NONE-mapped page is not writable (exceptions with FOLL_FORCE + * apply). get_user_pages_fast_only() always implicitly honors NUMA + * hinting faults. + */ + FOLL_HONOR_NUMA_FAULT = 1 << 12, /* See also internal only FOLL flags in mm/internal.h */ }; diff --git a/mm/gup.c b/mm/gup.c index 2493ffa10f4b..f463d3004ddc 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -597,7 +597,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, pte = ptep_get(ptep); if (!pte_present(pte)) goto no_page; - if (pte_protnone(pte) && !gup_can_follow_protnone(flags)) + if (pte_protnone(pte) && !gup_can_follow_protnone(vma, flags)) goto no_page; page = vm_normal_page(vma, address, pte); @@ -714,7 +714,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, if (likely(!pmd_trans_huge(pmdval))) return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); - if (pmd_protnone(pmdval) && !gup_can_follow_protnone(flags)) + if (pmd_protnone(pmdval) && !gup_can_follow_protnone(vma, flags)) return no_page_table(vma, flags); ptl = pmd_lock(mm, pmd); @@ -844,6 +844,10 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, if (WARN_ON_ONCE(foll_flags & FOLL_PIN)) return NULL; + /* + * We never set FOLL_HONOR_NUMA_FAULT because callers don't expect + * to fail on PROT_NONE-mapped pages. + */ page = follow_page_mask(vma, address, foll_flags, &ctx); if (ctx.pgmap) put_dev_pagemap(ctx.pgmap); @@ -2240,6 +2244,12 @@ static bool is_valid_gup_args(struct page **pages, int *locked, gup_flags |= FOLL_UNLOCKABLE; } + /* + * For now, always trigger NUMA hinting faults. Some GUP users like + * KVM really require it to benefit from autonuma. + */ + gup_flags |= FOLL_HONOR_NUMA_FAULT; + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) == (FOLL_PIN | FOLL_GET))) @@ -2564,7 +2574,14 @@ static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, struct page *page; struct folio *folio; - if (pte_protnone(pte) && !gup_can_follow_protnone(flags)) + /* + * Always fallback to ordinary GUP on PROT_NONE-mapped pages: + * pte_access_permitted() better should reject these pages + * either way: otherwise, GUP-fast might succeed in + * cases where ordinary GUP would fail due to VMA access + * permissions. + */ + if (pte_protnone(pte)) goto pte_unmap; if (!pte_access_permitted(pte, flags & FOLL_WRITE)) @@ -2983,8 +3000,8 @@ static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned lo if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) || pmd_devmap(pmd))) { - if (pmd_protnone(pmd) && - !gup_can_follow_protnone(flags)) + /* See gup_pte_range() */ + if (pmd_protnone(pmd)) return 0; if (!gup_huge_pmd(pmd, pmdp, addr, next, flags, @@ -3164,7 +3181,7 @@ static int internal_get_user_pages_fast(unsigned long start, if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | FOLL_FORCE | FOLL_PIN | FOLL_GET | FOLL_FAST_ONLY | FOLL_NOFAULT | - FOLL_PCI_P2PDMA))) + FOLL_PCI_P2PDMA | FOLL_HONOR_NUMA_FAULT))) return -EINVAL; if (gup_flags & FOLL_PIN) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 2e2e8a24cc71..2cd3e5502180 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1468,7 +1468,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, return ERR_PTR(-EFAULT); /* Full NUMA hinting faults to serialise migration in fault paths */ - if (pmd_protnone(*pmd) && !gup_can_follow_protnone(flags)) + if (pmd_protnone(*pmd) && !gup_can_follow_protnone(vma, flags)) return NULL; if (!pmd_write(*pmd) && gup_must_unshare(vma, flags, page))