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 X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D0CAC433DF for ; Wed, 1 Jul 2020 17:30:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5EAFA2078A for ; Wed, 1 Jul 2020 17:30:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5EAFA2078A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 004738D0054; Wed, 1 Jul 2020 13:30:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EF6518D0016; Wed, 1 Jul 2020 13:30:08 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DE4878D0054; Wed, 1 Jul 2020 13:30:08 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0244.hostedemail.com [216.40.44.244]) by kanga.kvack.org (Postfix) with ESMTP id C73C38D0016 for ; Wed, 1 Jul 2020 13:30:08 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 2A72E1EF2 for ; Wed, 1 Jul 2020 17:30:08 +0000 (UTC) X-FDA: 76990195296.28.coast01_1f1158226e82 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id 01BA56D64 for ; Wed, 1 Jul 2020 17:30:07 +0000 (UTC) X-HE-Tag: coast01_1f1158226e82 X-Filterd-Recvd-Size: 3948 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf48.hostedemail.com (Postfix) with ESMTP for ; Wed, 1 Jul 2020 17:30:07 +0000 (UTC) Received: from gaia (unknown [95.146.230.158]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CAE4020771; Wed, 1 Jul 2020 17:30:04 +0000 (UTC) Date: Wed, 1 Jul 2020 18:30:02 +0100 From: Catalin Marinas To: Andrew Morton Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Vincenzo Frascino , Szabolcs Nagy , Kevin Brodsky , Andrey Konovalov , Peter Collingbourne , Steven Price Subject: Re: [PATCH v5 06/25] mm: Add PG_ARCH_2 page flag Message-ID: <20200701173001.GG5191@gaia> References: <20200624175244.25837-1-catalin.marinas@arm.com> <20200624175244.25837-7-catalin.marinas@arm.com> <20200624113307.6165b3db2404c9d37b870a90@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200624113307.6165b3db2404c9d37b870a90@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: 01BA56D64 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 Wed, Jun 24, 2020 at 11:33:07AM -0700, Andrew Morton wrote: > On Wed, 24 Jun 2020 18:52:25 +0100 Catalin Marinas wrote: > > From: Steven Price > > For arm64 MTE support it is necessary to be able to mark pages that > > contain user space visible tags that will need to be saved/restored e.g. > > when swapped out. > > > > To support this add a new arch specific flag (PG_ARCH_2) that arch code > > can opt into using ARCH_USES_PG_ARCH_2. > > > > ... > > > > --- a/fs/proc/page.c > > +++ b/fs/proc/page.c > > @@ -217,6 +217,9 @@ u64 stable_page_flags(struct page *page) > > u |= kpf_copy_bit(k, KPF_PRIVATE_2, PG_private_2); > > u |= kpf_copy_bit(k, KPF_OWNER_PRIVATE, PG_owner_priv_1); > > u |= kpf_copy_bit(k, KPF_ARCH, PG_arch_1); > > +#ifdef CONFIG_ARCH_USES_PG_ARCH_2 > > + u |= kpf_copy_bit(k, KPF_ARCH_2, PG_arch_2); > > +#endif > > Do we need CONFIG_ARCH_USES_PG_ARCH_2? What would be the downside to > giving every architecture a PG_arch_2, but only arm64 uses it (at > present)? It turns out we have another issue with this flag. PG_arch_2 in the arm64 MTE patches is used to mark a page as having valid tags. During set_pte_at(), if the mapping type is tagged, we set PG_arch_2 (also setting it in other cases like copy_page). In combination with THP and swap (and some stress-testing to force swap-out), the kernel ends up clearing PG_arch_2 in __split_huge_page_tail(), causing a subsequent set_pte_at() to zero valid tags stored by user. The quick fix is to add an arch_huge_page_flags_split_preserve macro (need to think of a shorter name) which adds 1L << PG_arch_2 to the preserve list in the above mentioned function. However, I wonder whether it's safe to add both PG_arch_1 and PG_arch_2 to this list. At least on arm and arm64, PG_arch_1 is used to mark a page as D-cache clean (and don't need to do this again after splitting a pmd): diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 78c84bee7e29..22b3236a6dd8 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2364,6 +2364,10 @@ static void __split_huge_page_tail(struct page *head, int tail, (1L << PG_workingset) | (1L << PG_locked) | (1L << PG_unevictable) | + (1L << PG_arch_1) | +#ifdef CONFIG_64BIT + (1L << PG_arch_2) | +#endif (1L << PG_dirty))); /* ->mapping in first tail page is compound_mapcount */ Thanks. -- Catalin