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=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 59C2FC43381 for ; Wed, 27 Mar 2019 07:54:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 292C420811 for ; Wed, 27 Mar 2019 07:54:47 +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="R2NAJSEb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726359AbfC0Hyq (ORCPT ); Wed, 27 Mar 2019 03:54:46 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:55596 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725763AbfC0Hyp (ORCPT ); Wed, 27 Mar 2019 03:54:45 -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=DZ9/Ue7HNRbk1aTbbT+Yo5wt9wx5JG/3ryNtYzLGuvg=; b=R2NAJSEbEyHqA2tbnDYpQrPie b97a3pqcJL1/0r9in7/Wo4N2lf6SF3zrlISxxsCcfI/BXfLaKa5f38+izY2a3Bu46BOFMzNvluRYA CGAJXzCDrr5qtTJDuHCO6EgTlKzDupx0ttE/XMd0vjuRzdWRTNGTJP58uYL3d8cH3tuEt1EevHHvx yYz/f/kdkk80dNBqXhqDSieXNbwu1lQAFyDKzPjrnGJ0UubAK8/MeiESSSxZ9U0RdByVpBX6K98vV fb7ZaixOABzrLAqk5CXLJ53vPzT943oSHBCUA0zQKP3sVGPPtKU/1Vbn+Kfi8Yvh/vpxA2JsHfb0G tE8ZDvNbw==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1h93OT-0001DD-Fo; Wed, 27 Mar 2019 07:54:41 +0000 Date: Wed, 27 Mar 2019 00:54:41 -0700 From: Christoph Hellwig To: Anup Patel Cc: Christoph Hellwig , Palmer Dabbelt , Anup Patel , "linux-kernel@vger.kernel.org" , Mike Rapoport , Atish Patra , Albert Ou , Paul Walmsley , "linux-riscv@lists.infradead.org" Subject: Re: [PATCH v3 4/4] RISC-V: Allow booting kernel from any 4KB aligned address Message-ID: <20190327075441.GA29894@infradead.org> References: <20190325092234.5451-1-anup.patel@wdc.com> <20190325092234.5451-5-anup.patel@wdc.com> <20190325113935.GD27843@infradead.org> <20190325145919.GB14826@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) 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 Mon, Mar 25, 2019 at 09:46:59PM +0530, Anup Patel wrote: > > Why do you even care about kernel mappings for non-existant ram. > > We care because there will always be some buggy kernel driver/code going > out-of-bound and accessing non-existent RAM. If we by default map all > possible kernel virtual address then behaviour of buggy accesses will be > unpredictable. > > Further, I think we should also make .text and .rodata sections of kernel > as read-only. This will protect kernel code and rodata. All of that is useful at the final_setup_vm() time - but none of it matters during early setup_vm where life is complicated. Mike suggested on the previous iteration that you only do smaller mappings when setting up the final mapping to avoid the ops churn, and I fully agree with him. So I would suggest we avoid complicated the fiddly early boot changes that just add complxity, and you instead redirect your efforts to say implemented proper ro and non-executable sections using 4k mappings in the final VM setup only. That should actuall lead to less code and complexity, and provide more benefits.