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 22F07C433EF for ; Thu, 16 Dec 2021 05:51:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 864286B0078; Thu, 16 Dec 2021 00:51:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 813716B007B; Thu, 16 Dec 2021 00:51:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6DBCE6B007D; Thu, 16 Dec 2021 00:51:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0090.hostedemail.com [216.40.44.90]) by kanga.kvack.org (Postfix) with ESMTP id 5F2B76B0078 for ; Thu, 16 Dec 2021 00:51:11 -0500 (EST) Received: from smtpin10.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 274EE8771A for ; Thu, 16 Dec 2021 05:51:01 +0000 (UTC) X-FDA: 78922583922.10.E50358F Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf04.hostedemail.com (Postfix) with ESMTP id BB9E240014 for ; Thu, 16 Dec 2021 05:51:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639633859; 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=XJ16aaddk0IskgGChPHNllZ5/FTCKcwfaGzYXjxHG3s=; b=bWzfwrmZz945s37a3ECPe2AChqdqWXWDObHssEAUc7aPQUQGxHIb2uWexqEkBe67TKrwcy xlErwXD9aNzf70D6SxtAdSS2eFP6R9oR6mD0HBogDoTOrvimQXH+wE5+FqnqMg5XJA/ejg j4t1LpclGWn64eFA67hYH+GfaZ09nFc= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-55-qwqHKKRQM6yH9WDRgNZnDA-1; Thu, 16 Dec 2021 00:50:58 -0500 X-MC-Unique: qwqHKKRQM6yH9WDRgNZnDA-1 Received: by mail-wm1-f71.google.com with SMTP id n16-20020a05600c3b9000b003331973fdbbso9872583wms.0 for ; Wed, 15 Dec 2021 21:50:58 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=XJ16aaddk0IskgGChPHNllZ5/FTCKcwfaGzYXjxHG3s=; b=33qSaELzu++CbI5c45IizU1qpy8febxoNGC387rCZJNuEWFDGBTgujeQKkvkZ8Jdez 5QLivMi8PBkKSCuObucD+08EsELa9r/FGnsi0U6TzjnHPfI478fK0ily1tMaIdVem4AI 8E02VmjdrkyypKZ2znqUGeOI5H9a2XQ3vByqJucQYYUow5F8c+cQEWEWUC9hw+4gTMzp pv0HnN5xmXzVDlgLYhnO7ZiktxiD7HSo1020MruFwrJLUAJcpUNyFu3eKs7C8DsGs4k7 fDrblQlAcyZ7O6yWC1YiDyGKUv0lm83KKd1gMFpbJR2tlmJ5Tb8+s+7wzSE8krIaFVYQ JdbA== X-Gm-Message-State: AOAM533XMQVdiaL4xlSdnQQPAbKfGGyvzR8ziFlA/y4Ao6Y6ehfuybei ud1kWgBsPozKKvOOgpHyOeZe4N2bkTJjkDFRqetKE5KgZVw7Mzk38zmBNPsEQusO2zrQRiOCn8L Dqpe53MaGKRE= X-Received: by 2002:a05:600c:3c8a:: with SMTP id bg10mr3377322wmb.106.1639633857715; Wed, 15 Dec 2021 21:50:57 -0800 (PST) X-Google-Smtp-Source: ABdhPJzTNseQ2yXKap40Rqqicn+6SuZGW7QXCaMxBJD7KzDF0oiX8vRTe84g8uFp+8cFIQT9hrGDfg== X-Received: by 2002:a05:600c:3c8a:: with SMTP id bg10mr3377261wmb.106.1639633856467; Wed, 15 Dec 2021 21:50:56 -0800 (PST) Received: from xz-m1.local ([64.64.123.12]) by smtp.gmail.com with ESMTPSA id r7sm3701875wrq.29.2021.12.15.21.50.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Dec 2021 21:50:55 -0800 (PST) Date: Thu, 16 Dec 2021 13:50:47 +0800 From: Peter Xu To: Alistair Popple Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Axel Rasmussen , Nadav Amit , Mike Rapoport , Hugh Dickins , Mike Kravetz , "Kirill A . Shutemov" , Jerome Glisse , Matthew Wilcox , Andrew Morton , David Hildenbrand , Andrea Arcangeli Subject: Re: [PATCH v6 03/23] mm: Check against orig_pte for finish_fault() Message-ID: References: <20211115075522.73795-1-peterx@redhat.com> <20211115075522.73795-4-peterx@redhat.com> <6260997.DYpkEd5BTb@nvdebian> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BB9E240014 X-Stat-Signature: 4c334u7c1jaaz5tx7fa3q4z4yxomnpgr Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=bWzfwrmZ; spf=none (imf04.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1639633860-337217 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 Thu, Dec 16, 2021 at 01:38:33PM +0800, Peter Xu wrote: > On Thu, Dec 16, 2021 at 04:01:47PM +1100, Alistair Popple wrote: > > On Monday, 15 November 2021 6:55:02 PM AEDT Peter Xu wrote: > > > We used to check against none pte and in those cases orig_pte should always be > > > none pte anyway. > > > > Is that always true? From what I can see in handle_pte_fault() orig_pte only > > gets initialised in the !pmd_none() case so might not be pte_none. > > I believe it's true, otherwise I must have overlooked. > > IMHO it's not "when we set orig_pte" that matters - note that finish_fault() > (that this patch modifies) is only called for file-backed memories, and it's > only called in do_fault() where the pte is not mapped at all. > > DAX seems to call it too, but still DAX comes from do_fault() too, afaict. > > The pte will not be mapped in two cases in handle_pte_fault(): > > - When pmd_none > > - When !pmd_none, however if we find that pte_none==true, that's: > > if (pte_none(vmf->orig_pte)) { > pte_unmap(vmf->pte); > vmf->pte = NULL; > } > > So when we're already in do_fault(), afaict, orig_pte must be pte_none(). > Another side note is that, IIUC pte_none() is a looser check than the > pte_val()==0 and it should be arch dependent. So one more thing I forgot to mention... Of course above is based on the fact that orig_pte will be initialized to zero when creating vmf structure, and that's done in __handle_mm_fault(): struct vm_fault vmf = { .vma = vma, .address = address & PAGE_MASK, .flags = flags, .pgoff = linear_page_index(vma, address), .gfp_mask = __get_fault_gfp_mask(vma), }; I'm not sure whether I should explicitly set it to pte_val(0), in most C programs we'll already assume it's a proper reset of orig_pte value in c99 initialization format, but if anyone thinks we should do that explicitly plus some comments I can do that too. > > Thanks, > > > > > > This change prepares us to be able to call do_fault() on !none ptes. For > > > example, we should allow that to happen for pte marker so that we can restore > > > information out of the pte markers. > > > > > > Signed-off-by: Peter Xu > > > --- > > > mm/memory.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/mm/memory.c b/mm/memory.c > > > index 04662b010005..d5966d9e24c3 100644 > > > --- a/mm/memory.c > > > +++ b/mm/memory.c > > > @@ -4052,7 +4052,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf) > > > vmf->address, &vmf->ptl); > > > ret = 0; > > > /* Re-check under ptl */ > > > - if (likely(pte_none(*vmf->pte))) > > > + if (likely(pte_same(*vmf->pte, vmf->orig_pte))) > > > do_set_pte(vmf, page, vmf->address); > > > else > > > ret = VM_FAULT_NOPAGE; > > > > > > > > > > > > > -- > Peter Xu -- Peter Xu