From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 22 Oct 2014 22:42:12 +0200 (CEST) Received: from localhost.localdomain ([127.0.0.1]:41219 "EHLO linux-mips.org" rhost-flags-OK-OK-OK-FAIL) by eddie.linux-mips.org with ESMTP id S27012171AbaJVUmKhGcQJ (ORCPT ); Wed, 22 Oct 2014 22:42:10 +0200 Received: from scotty.linux-mips.net (localhost.localdomain [127.0.0.1]) by scotty.linux-mips.net (8.14.8/8.14.8) with ESMTP id s9MKg9CG017586; Wed, 22 Oct 2014 22:42:09 +0200 Received: (from ralf@localhost) by scotty.linux-mips.net (8.14.8/8.14.8/Submit) id s9MKg9G6017585; Wed, 22 Oct 2014 22:42:09 +0200 Date: Wed, 22 Oct 2014 22:42:09 +0200 From: Ralf Baechle To: "Maciej W. Rozycki" Cc: David Daney , linux-mips@linux-mips.org, Ben Hutchings Subject: Re: Single MIPS kernel Message-ID: <20141022204209.GE12502@linux-mips.org> References: <20141022083437.GB18581@linux-mips.org> <5447EFB5.4090009@gmail.com> <20141022190515.GC12502@linux-mips.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 43504 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Wed, Oct 22, 2014 at 08:19:07PM +0100, Maciej W. Rozycki wrote: > > > Another reason is that the protocol between the bootloader and the kernel > > > varies by platform. So you would have to have several different entry > > > points, one for each booting protocol. > > > > > > I am not sure how the bootloaders would know which entry point to use. > > > > That's where I foresaw the needs for the ISA style platform probe right > > at the kernel entry point before fanning out to a platform-specific > > entry point. > > > > Since we already support compressed kernels I'm wondering if relocation > > might also be performed by the compression wrapper along with the > > hardware probe. That would leave the vmlinux itself untouched and > > the wrapper could be installed on the target. > > Wouldn't it make sense to make a unified kernel virtually mapped? That > would avoid the issue with RAM being present at different locations across > systems and also if big pages were used, that I believe are available > almost universally across the MIPS family, any performance hit would be > minimal. There would be hardly any increase in the binary image size too. > Run-time mappings such as `kmalloc' or `ioremap' could continue using > unmapped segments. I think some MIPS III CPUs were restricted to just 4MB max. page size. NEC VR4xxx I think. Still a pair would map 8MB which on the affected small memory systems should suffice. 16MB, 64MB are more typical sizes. R3000 is a different kettle. To 4k or not to 4k is not a question ;-) Now mapping the kernel alone wouldn't solve the security issue mentioned by David. The image would still lie around in KSEG0 / XKPHYS for whatever wants to run over so that should ideally also be a flexible address. Otoh the mapped kernel certainly would have the lowest size overhead. I have faint memories of restrictions for TLB instructions or was it TLB exception handlers into mapped space, would have to do some rtfming on that topic. Years ago I did test the impact of one less available TLB entry with lmbench; the loss was around 2%. That was on a CPU with 64 entries. Ralf