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 3EBFCC433EF for ; Thu, 24 Feb 2022 12:33:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234424AbiBXMeS (ORCPT ); Thu, 24 Feb 2022 07:34:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234416AbiBXMeP (ORCPT ); Thu, 24 Feb 2022 07:34:15 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E84D02804C0 for ; Thu, 24 Feb 2022 04:33:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645706020; 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=QWdKc7kD/Q/4rS5vi3P5eDrUhZz3GFyt+nP81Uz1mas=; b=P1tQ5Ll7hiii5uu3wKncxuZd29lz+P8M1FcAPqbqtG2Ax6yrQccTuslGZran0Q4YOS8orO 5ZCSSUdK5BHICaxtoNDopsglmnLM8NnonuxsTvFVj+WoG9l+ca/P3Nia4ndl/MnqJKn/ur vm3YTgNT7AHwqIcnlQ7UPzcMxdUZRuU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-139-_LaSqInlMl2xFN2Y1YreTQ-1; Thu, 24 Feb 2022 07:33:34 -0500 X-MC-Unique: _LaSqInlMl2xFN2Y1YreTQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2B00651EA; Thu, 24 Feb 2022 12:33:31 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id 18FB52635E; Thu, 24 Feb 2022 12:32:54 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , Pedro Gomes , Oded Gabbay , linux-mm@kvack.org, David Hildenbrand Subject: [PATCH RFC 10/13] mm/gup: disallow follow_page(FOLL_PIN) Date: Thu, 24 Feb 2022 13:26:11 +0100 Message-Id: <20220224122614.94921-11-david@redhat.com> In-Reply-To: <20220224122614.94921-1-david@redhat.com> References: <20220224122614.94921-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We want to change the way we handle R/O pins on anonymous pages that might be shared: if we detect a possibly shared anonymous page -- mapped R/O and not !PageAnonExclusive() -- we want to trigger unsharing via a page fault, resulting in an exclusive anonymous page that can be pinned reliably without getting replaced via COW on the next write fault. However, the required page fault will be problematic for follow_page(): in contrast to ordinary GUP, follow_page() doesn't trigger faults internally. So we would have to end up failing a R/O pin via follow_page(), although there is something mapped R/O into the page table, which might be rather surprising. We don't seem to have follow_page(FOLL_PIN) users, and it's a purely internal MM function. Let's just make our life easier and the semantics of follow_page() clearer by just disallowing FOLL_PIN for follow_page() completely. Signed-off-by: David Hildenbrand --- mm/gup.c | 3 +++ mm/hugetlb.c | 8 +++++--- 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index a9d4d724aef7..7127e789d210 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -875,6 +875,9 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, if (vma_is_secretmem(vma)) return NULL; + if (foll_flags & FOLL_PIN) + return NULL; + page = follow_page_mask(vma, address, foll_flags, &ctx); if (ctx.pgmap) put_dev_pagemap(ctx.pgmap); diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 0c2f3d500487..8aaca8becf97 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6693,9 +6693,11 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, spinlock_t *ptl; pte_t pte; - /* FOLL_GET and FOLL_PIN are mutually exclusive. */ - if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == - (FOLL_PIN | FOLL_GET))) + /* + * FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via + * follow_hugetlb_page(). + */ + if (WARN_ON_ONCE(flags & FOLL_PIN)) return NULL; retry: -- 2.35.1