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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 1A276C433FF for ; Fri, 9 Aug 2019 11:45:08 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D9F472166E for ; Fri, 9 Aug 2019 11:45:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="e62Bqoer" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D9F472166E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=y83uJcnZpzxmm0sidb73pDzU0r6BKNkzEZ/51dy3hb8=; b=e62BqoerdYOY9L sEjHmgTmV+SLuGLDNmcbx9dy4bxnCq8sGflVIEG7hYCraQad65VKzBbKSFzm7w197KoX5Goj92Kfy uo/Rktg2szh7KZfdngo1uzqSZd0ZLIZ5lVccQ4id/BFFPqcpPLdFU7XzqIXr41r3+Sf4iSita0kd3 gdRd0cuKvtX2zV6kzDYuMQtlsdae4YN/hvJM/g5LDP4gtGQOmR5bp2tKZLARWAqwWtUK5hMQNcMjP /Ew6+mx5lo8itBsVpnCqRYTaDOl3eCfxXYN6CnsnESW9Pl203CJfPi3UDQH/4htoUU16O1oe3PlDy Jo++F1ASG08Eh5wrGzGA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hw3KO-00078y-Rk; Fri, 09 Aug 2019 11:45:00 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hw3KM-00078a-IG; Fri, 09 Aug 2019 11:44:59 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C12CD1596; Fri, 9 Aug 2019 04:44:57 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1DD783F575; Fri, 9 Aug 2019 04:44:53 -0700 (PDT) Date: Fri, 9 Aug 2019 12:44:51 +0100 From: Mark Rutland To: Matthew Wilcox Subject: Re: [RFC V2 0/1] mm/debug: Add tests for architecture exported page table helpers Message-ID: <20190809114450.GF48423@lakrids.cambridge.arm.com> References: <1565335998-22553-1-git-send-email-anshuman.khandual@arm.com> <20190809101632.GM5482@bombadil.infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190809101632.GM5482@bombadil.infradead.org> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190809_044458_644311_50D9CF79 X-CRM114-Status: GOOD ( 13.53 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Tetsuo Handa , James Hogan , Heiko Carstens , Michal Hocko , linux-mm@kvack.org, Paul Mackerras , sparclinux@vger.kernel.org, Thomas Gleixner , linux-s390@vger.kernel.org, Michael Ellerman , x86@kernel.org, Russell King - ARM Linux , Steven Price , Jason Gunthorpe , linux-arm-kernel@lists.infradead.org, linux-snps-arc@lists.infradead.org, Kees Cook , Anshuman Khandual , Masahiro Yamada , Mark Brown , Dan Williams , Vlastimil Babka , Sri Krishna chowdary , Ard Biesheuvel , Greg Kroah-Hartman , Dave Hansen , linux-mips@vger.kernel.org, Ralf Baechle , linux-kernel@vger.kernel.org, Peter Zijlstra , Mike Rapoport , Paul Burton , Vineet Gupta , Martin Schwidefsky , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Aug 09, 2019 at 03:16:33AM -0700, Matthew Wilcox wrote: > On Fri, Aug 09, 2019 at 01:03:17PM +0530, Anshuman Khandual wrote: > > Should alloc_gigantic_page() be made available as an interface for general > > use in the kernel. The test module here uses very similar implementation from > > HugeTLB to allocate a PUD aligned memory block. Similar for mm_alloc() which > > needs to be exported through a header. > > Why are you allocating memory at all instead of just using some > known-to-exist PFNs like I suggested? IIUC the issue is that there aren't necessarily known-to-exist PFNs that are sufficiently aligned -- they may not even exist. For example, with 64K pages, a PMD covers 512M. The kernel image is (generally) smaller than 512M, and will be mapped at page granularity. In that case, any PMD entry for a kernel symbol address will point to the PTE level table, and that will only necessarily be page-aligned, as any P?D level table is only necessarily page-aligned. In the same configuration, you could have less than 512M of total memory, and none of this memory is necessarily aligned to 512M. So beyond the PTE level, I don't think you can guarantee a known-to-exist valid PFN. I also believe that synthetic PFNs could fail pfn_valid(), so that might cause us pain too... Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel