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=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 C28ECC43381 for ; Fri, 1 Mar 2019 13:39:43 +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 925CF2084D for ; Fri, 1 Mar 2019 13:39:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="F/6K2ncQ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 925CF2084D 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:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=52fo5WoKIJYtkk2lHKm5NO+lUaKEFIz6y+owt/KC2e4=; b=F/6K2ncQeU1UJi FCVfjA/uUN1gBq+z93P5gzqN1IZ2onONeTCBxdNmQtrAXyN8hdWeiOFdy8IfbLE/kSekpU53wgS+C D6AGrggaodRDU1wF+MjkhUOly69BcIXI90QjF+JVgTRklrExneRkoQEvg+eVvo8VXwVRK7YTk+nbf 5zRRtjtsRYFEhbnHIClmkVov8Gw0YGavrW/Ewt3nf1OlKGV8ISi5Qo2VFPXuW8Wa3pFB3fyEf+lHn nIw1HeU6kC1o8PQ7Xq99F1ne+PTLkxX0s6E+Hz48Be9cE5WTRwhTOxuRlpPo7opLeEKSMaIJmVyUh gVwBE8PB7713F2VuXlFg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gziO3-0003tV-0x; Fri, 01 Mar 2019 13:39:39 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gziNz-0003sm-Jy for linux-arm-kernel@lists.infradead.org; Fri, 01 Mar 2019 13:39:37 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6111CA78; Fri, 1 Mar 2019 05:39:35 -0800 (PST) Received: from [10.1.196.69] (e112269-lin.cambridge.arm.com [10.1.196.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 19B2E3F5C1; Fri, 1 Mar 2019 05:39:31 -0800 (PST) Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros To: "Kirill A. Shutemov" , Mike Rapoport References: <20190221113502.54153-1-steven.price@arm.com> <20190221113502.54153-4-steven.price@arm.com> <20190221142812.oa53lfnnfmsuh6ys@kshutemo-mobl1> <20190221145706.zqwfdoyiirn3lc7y@kshutemo-mobl1> <20190221210618.voyfs5cnafpvgedh@kshutemo-mobl1> <20190301115300.GE5156@rapoport-lnx> <20190301123031.rw3dswcoaa2x7haq@kshutemo-mobl1> From: Steven Price Message-ID: Date: Fri, 1 Mar 2019 13:39:30 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190301123031.rw3dswcoaa2x7haq@kshutemo-mobl1> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190301_053935_662155_1E9F1477 X-CRM114-Status: GOOD ( 18.49 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Dave Hansen , Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , x86@kernel.org, Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , James Morse , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, "Liang, Kan" 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 01/03/2019 12:30, Kirill A. Shutemov wrote: > On Fri, Mar 01, 2019 at 01:53:01PM +0200, Mike Rapoport wrote: >> Him Kirill, >> >> On Fri, Feb 22, 2019 at 12:06:18AM +0300, Kirill A. Shutemov wrote: >>> On Thu, Feb 21, 2019 at 05:16:46PM +0000, Steven Price wrote: >>>>>> Note that in terms of the new page walking code, these new defines are >>>>>> only used when walking a page table without a VMA (which isn't currently >>>>>> done), so architectures which don't use p?d_large currently will work >>>>>> fine with the generic versions. They only need to provide meaningful >>>>>> definitions when switching to use the walk-without-a-VMA functionality. >>>>> >>>>> How other architectures would know that they need to provide the helpers >>>>> to get walk-without-a-VMA functionality? This looks very fragile to me. >>>> >>>> Yes, you've got a good point there. This would apply to the p?d_large >>>> macros as well - any arch which (inadvertently) uses the generic version >>>> is likely to be fragile/broken. >>>> >>>> I think probably the best option here is to scrap the generic versions >>>> altogether and simply introduce a ARCH_HAS_PXD_LARGE config option which >>>> would enable the new functionality to those arches that opt-in. Do you >>>> think this would be less fragile? >>> >>> These helpers are useful beyond pagewalker. >>> >>> Can we actually do some grinding and make *all* archs to provide correct >>> helpers? Yes, it's tedious, but not that bad. >> >> Many architectures simply cannot support non-leaf entries at the higher >> levels. I think letting the use a generic helper actually does make sense. > > I disagree. > > It's makes sense if the level doesn't exists on the arch. This is what patch 24 [1] of the series does - if the level doesn't exist then appropriate stubs are provided. > But if the level exists, it will be less frugile to ask the arch to > provide the helper. Even if it is dummy always-false. The problem (as I see it), is we need a reliable set of p?d_large() implementations to be able to walk arbitrary page tables. Either the entire functionality of walking page tables without a VMA has to be an opt-in per architecture, or we need to mandate that every architecture provide these implementations. I could provide an asm-generic header to provide a complete set of dummy implementations for architectures that don't support large pages at all, but that seems a bit overkill when most architectures only need to define 2 or 3 implementations (the rest being provided by the folded-levels automatically). Thanks, Steve [1] https://lore.kernel.org/lkml/20190227170608.27963-25-steven.price@arm.com/ _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel