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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 D9143C3A59F for ; Mon, 26 Aug 2019 13:13:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B04482186A for ; Mon, 26 Aug 2019 13:13:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="S0Qm85v5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731513AbfHZNNt (ORCPT ); Mon, 26 Aug 2019 09:13:49 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:59236 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731174AbfHZNNt (ORCPT ); Mon, 26 Aug 2019 09:13:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=urDTYQxxHpDLHKYV3DkLPJyBgIdOzd8vbZl6Cfapxyc=; b=S0Qm85v5u+mC94Z+1NTp3zLxy RVikWlbB8+mD7D3i6pKW1vaRh6+mpvdmY0hZwt7QeNMOfDK4v1mKu4uLruFJY+80WEeNiclw0bMni VgFWVa4FMxmnuDh4DG/NHs34XNaySiBjcLQotEzPIlKfk98LzJOfOfATotjcOvgRsK0BvJg1vvrY6 PC3VQkaRupcuqt52WqBPC5JvmCjmjjLmU1rbYgod7HJ/IZrUNwVg/kxESAnrEZvrP/71g/C/cTVL3 KSmHw9glYY9tQdIrKjhRnF9olVe6RlSSQh43S7mnoLe1VnIU+Q8j9tFnodpiFcOU1xeFxRbNIYZHd 4Bsb3y2yA==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1i2Eo0-0002Mw-Mf; Mon, 26 Aug 2019 13:13:08 +0000 Date: Mon, 26 Aug 2019 06:13:08 -0700 From: Matthew Wilcox To: Anshuman Khandual Cc: linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Greg Kroah-Hartman , Thomas Gleixner , Mike Rapoport , Jason Gunthorpe , Dan Williams , Peter Zijlstra , Michal Hocko , Mark Rutland , Mark Brown , Steven Price , Ard Biesheuvel , Masahiro Yamada , Kees Cook , Tetsuo Handa , Sri Krishna chowdary , Dave Hansen , Russell King - ARM Linux , Michael Ellerman , Paul Mackerras , Martin Schwidefsky , Heiko Carstens , "David S. Miller" , Vineet Gupta , James Hogan , Paul Burton , Ralf Baechle , linux-snps-arc@lists.infradead.org, linux-mips@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC V2 0/1] mm/debug: Add tests for architecture exported page table helpers Message-ID: <20190826131308.GA15933@bombadil.infradead.org> References: <1565335998-22553-1-git-send-email-anshuman.khandual@arm.com> <20190809101632.GM5482@bombadil.infradead.org> <20190809135202.GN5482@bombadil.infradead.org> <7a88f6bb-e8c7-3ac7-2f92-1de752a01f33@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7a88f6bb-e8c7-3ac7-2f92-1de752a01f33@arm.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Mon, Aug 26, 2019 at 08:07:13AM +0530, Anshuman Khandual wrote: > On 08/09/2019 07:22 PM, Matthew Wilcox wrote: > > On Fri, Aug 09, 2019 at 04:05:07PM +0530, Anshuman Khandual wrote: > >> On 08/09/2019 03:46 PM, 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? > >> > >> We needed PFN to be PUD aligned for pfn_pud() and PMD aligned for mk_pmd(). > >> Now walking the kernel page table for a known symbol like kernel_init() > > > > I didn't say to walk the kernel page table. I said to call virt_to_pfn() > > for a known symbol like kernel_init(). > > > >> as you had suggested earlier we might encounter page table page entries at PMD > >> and PUD which might not be PMD or PUD aligned respectively. It seemed to me > >> that alignment requirement is applicable only for mk_pmd() and pfn_pud() > >> which create large mappings at those levels but that requirement does not > >> exist for page table pages pointing to next level. Is not that correct ? Or > >> I am missing something here ? > > > > Just clear the bottom bits off the PFN until you get a PMD or PUD aligned > > PFN. It's really not hard. > > As Mark pointed out earlier that might end up being just a synthetic PFN > which might not even exist on a given system. And why would that matter?