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 05656C433FF for ; Fri, 2 Aug 2019 08:44:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEB0320657 for ; Fri, 2 Aug 2019 08:44:55 +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="QMntMBRp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404434AbfHBIoy (ORCPT ); Fri, 2 Aug 2019 04:44:54 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:56166 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730872AbfHBIoy (ORCPT ); Fri, 2 Aug 2019 04:44:54 -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=v00Ip7tFTxfOW7ci2f67H952n7pZPTilSNtqWzGu0Kc=; b=QMntMBRpF4JmUY3VNLhxAr9gu 9J7x8c1UZJylRbJCbHSbhFuOCugKaSW/zMuZ0MKqz3y9tQ7LCKVDIVgkb7mNgNgtBHuttyvui9yFC 10dYHUbbA2H8or9294FPrr9iobMHCelDY/LmJxnT7JH11SpB9uSMxJi7cpoOCbdHhzp1Dra+R9gfk 6BL2aH04Qh5ls+AZ1N9Xo5gxGTOBystLL95Khj4l99Qk1jH/VzMlPx1115zqRMBx5fHuDFXB6w263 T6BWWDcHTWE0XuYw6Lghmff+d9Kg6tDfMN0kHuGp/d1Uec+uQtYmgrAVOIf8FTEx+CwbvQmwEPr1C v/TQhHBfQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1htTBF-0000mV-5w; Fri, 02 Aug 2019 08:44:53 +0000 Date: Fri, 2 Aug 2019 01:44:53 -0700 From: Christoph Hellwig To: Paul Walmsley Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Alexandre Ghiti Subject: Re: [PATCH] riscv: kbuild: add virtual memory system selection Message-ID: <20190802084453.GA1410@infradead.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 26, 2019 at 01:00:49PM -0700, Paul Walmsley wrote: > > The RISC-V specifications currently define three virtual memory > translation systems: Sv32, Sv39, and Sv48. Sv32 is currently specific > to 32-bit systems; Sv39 and Sv48 are currently specific to 64-bit > systems. The current kernel only supports Sv32 and Sv39, but we'd > like to start preparing for Sv48. As an initial step, allow the > virtual memory translation system to be selected via kbuild, and stop > the build if an option is selected that the kernel doen't currently > support. > > This patch currently has no functional impact. It cause the user to be able to select a config which thus won't build. So it is not just useless, which already is a reason not to merge it, but actively harmful, which is even worse. Even if we assume we want to implement Sv48 eventually (which seems to be a bit off), we need to make this a runtime choice and not a compile time one to not balloon the number of configs that distributions (and kernel developers) need to support.