From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7EC3F1442FB for ; Mon, 29 Jul 2024 12:55:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722257740; cv=none; b=oEqp7OQgTRuAkzW6XjJHa14YIm5GNSTHC4o2UN0yIyuwyV9l3ymou0hBor3EzUYFXM0v1+Yyh+jdIMRrD4P0HQcuwHVZoZse3YcQuIRG5L0IOBb9OCUGvUB3dv7wpdkaMJbDUPa2ojJ6+kXpmuKdkfojGTBz1H/ZqiracmJHPaA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722257740; c=relaxed/simple; bh=ApFBGEKrXGZ5wlAkBjBHyCnfi54MpPWXk2MQoc3J3CQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VOxDpHEHIDLhlQkaQ9LKYzoh/PAAAQvterCwr9m2C1/VR/ZOwwat5XjX/RUFHh7PPWD4dJNbZZvNwTITAEvC6kA9tqNcntcfxCRsz7HuXA6hYRlGLHtLFJk/vM9CZDJuMRLZrDDyMcn7iKy/GOrlyWAnirPXfhCWC5ztXlC+et0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Z3h2O27S; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Z3h2O27S" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=opEWLaRlUPPuTcVF9JQV5B1iYQkixzeRREUKAI6824o=; b=Z3h2O27S0fXUvOG/m2g3CSn1iQ s0wXWD8/fD7spO399wDArSxC8+8WM2vk15vnvNiBv6IiUUHSBr7j1wOgH+gyZYk1O+oITdb2j7yeA Rb+Qu/d73aXY3LXHhGv+RKBJV6HVpjKUWVS/8k4EnXlbPw4tY5Jo063WyHGZJL/FFDOf5xZqWnU+r +1ZyDxJgj72Vr/WDgoM2E4Ek4HaXRc8cORZs/E6UJ91+7it71Y2soJiZtzYpZ6wz1DB/qx7BZxCrd H5deqH4KLMRAd6hUqLr5AEhf09bFQHflG8wdayykkjv2OexzpdKaziehGEe5AacQzrxzvgO/7HZlS aicELm1w==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sYPuN-0000000DZnp-1691; Mon, 29 Jul 2024 12:55:23 +0000 Date: Mon, 29 Jul 2024 13:55:23 +0100 From: Matthew Wilcox To: Chuanhua Han Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, ying.huang@intel.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, hughd@google.com, kaleshsingh@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, mhocko@suse.com, minchan@kernel.org, nphamcs@gmail.com, ryan.roberts@arm.com, senozhatsky@chromium.org, shakeel.butt@linux.dev, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, xiang@kernel.org, yosryahmed@google.com, Chuanhua Han Subject: Re: [PATCH v5 3/4] mm: support large folios swapin as a whole for zRAM-like swapfile Message-ID: References: <20240726094618.401593-1-21cnbao@gmail.com> <20240726094618.401593-4-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Jul 29, 2024 at 02:36:38PM +0800, Chuanhua Han wrote: > Matthew Wilcox 于2024年7月29日周一 11:51写道： > > > > On Fri, Jul 26, 2024 at 09:46:17PM +1200, Barry Song wrote: > > > - folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, > > > - vma, vmf->address, false); > > > + folio = alloc_swap_folio(vmf); > > > page = &folio->page; > > > > This is no longer correct. You need to set 'page' to the precise page > > that is being faulted rather than the first page of the folio. It was > > fine before because it always allocated a single-page folio, but now it > > must use folio_page() or folio_file_page() (whichever has the correct > > semantics for you). > > > > Also you need to fix your test suite to notice this bug. I suggest > > doing that first so that you know whether you've got the calculation > > correct. > > > > > > This is no problem now, we support large folios swapin as a whole, so > the head page is used here instead of the page that is being faulted. > You can also refer to the current code context, now support large > folios swapin as a whole, and previously only support small page > swapin is not the same. You have completely failed to understand the problem. Let's try it this way: We take a page fault at address 0x123456789000. If part of a 16KiB folio, that's page 1 of the folio at 0x123456788000. If you now map page 0 of the folio at 0x123456789000, you've given the user the wrong page! That looks like data corruption. The code in if (folio_test_large(folio) && folio_test_swapcache(folio)) { as Barry pointed out will save you -- but what if those conditions fail? What if the mmap has been mremap()ed and the folio now crosses a PMD boundary? mk_pte() will now be called on the wrong page.