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=-1.1 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 766DBC43381 for ; Thu, 21 Feb 2019 17:17:02 +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 434702083B for ; Thu, 21 Feb 2019 17:17:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ECzAOCds" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 434702083B 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=jlIzone9o0Xnpv8QFEngkefwYgD0BS16jrR9siymdW4=; b=ECzAOCds2EK2uc OL3nIKNg4ILC53jo/UZFEsG4IzGEIrAEsal2dEVqFCOIbPGCJQqsBNfwZmMED3/xrrtTqHlBhtnvI z7sC2+E8h7JZs2L6Km2emJsyUeMq/3y0WJJfpZirbP/unUqo+sCpQ3SZpz3K+x02J/6ZIZUde+rQ4 DfptVEok10+jPjmmxPvcdHK249PqhYiqw1ByEB9tc6muJwRk9ELVvCN97CDhWJ/WQJYWP4wfY5RZe pOprzNX0LuESJuyfvHJhROjBr9kGnxNXNNwp29cDpuKwVVHv0eB7Ui9rAcXFIq0InkC3EBhO6eMDq vjH3voHyMfsaGwFg36pA==; 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 1gwrxw-0005jB-T0; Thu, 21 Feb 2019 17:16:56 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gwrxt-0005if-FT for linux-arm-kernel@lists.infradead.org; Thu, 21 Feb 2019 17:16:54 +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 52E93A78; Thu, 21 Feb 2019 09:16:52 -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 A8D433F5C1; Thu, 21 Feb 2019 09:16:48 -0800 (PST) Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros To: "Kirill A. Shutemov" References: <20190221113502.54153-1-steven.price@arm.com> <20190221113502.54153-4-steven.price@arm.com> <20190221142812.oa53lfnnfmsuh6ys@kshutemo-mobl1> <20190221145706.zqwfdoyiirn3lc7y@kshutemo-mobl1> From: Steven Price Message-ID: Date: Thu, 21 Feb 2019 17:16:46 +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: <20190221145706.zqwfdoyiirn3lc7y@kshutemo-mobl1> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190221_091653_522107_B5C0C781 X-CRM114-Status: GOOD ( 21.18 ) 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 , x86@kernel.org, Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , Dave Hansen , 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 21/02/2019 14:57, Kirill A. Shutemov wrote: > On Thu, Feb 21, 2019 at 02:46:18PM +0000, Steven Price wrote: >> On 21/02/2019 14:28, Kirill A. Shutemov wrote: >>> On Thu, Feb 21, 2019 at 11:34:52AM +0000, Steven Price wrote: >>>> From: James Morse >>>> >>>> Exposing the pud/pgd levels of the page tables to walk_page_range() means >>>> we may come across the exotic large mappings that come with large areas >>>> of contiguous memory (such as the kernel's linear map). >>>> >>>> For architectures that don't provide p?d_large() macros, provided a >>>> does nothing default. >>> >>> Nak, sorry. >>> >>> Power will get broken by the patch. It has pmd_large() inline function, >>> that will be overwritten by the define from this patch. >>> >>> I believe it requires more ground work on arch side in general. >>> All architectures that has huge page support has to provide these helpers >>> (and matching defines) before you can use it in a generic code. >> >> Sorry about that, I had compile tested on power, but obviously not the >> right config to actually see the breakage. > > I don't think you'll catch it at compile-time. It would silently override > the helper with always-false. Ah, that might explain why I missed it. >> I'll do some grepping - hopefully this is just a case of exposing the >> functions/defines that already exist for those architectures. > > I see the same type of breakage on s390 and sparc. > >> 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? Thanks, Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel