From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id DDCDDDDEE7 for ; Mon, 8 Oct 2007 01:01:57 +1000 (EST) In-Reply-To: <18184.23379.478676.911097@cargo.ozlabs.ibm.com> References: <18184.23379.478676.911097@cargo.ozlabs.ibm.com> Mime-Version: 1.0 (Apple Message framework v752.2) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <796C20BF-1592-4F07-B83B-5EA35CADBA01@kernel.crashing.org> From: Kumar Gala Subject: Re: TASK_SIZE default 0x80000000 ? Date: Sun, 7 Oct 2007 10:02:04 -0500 To: Paul Mackerras Cc: PowerPC dev list , Benjamin Herrenschmidt List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Oct 6, 2007, at 11:06 PM, Paul Mackerras wrote: > Kumar Gala writes: > >> In a discussion with Hollis over beer he raised the question why >> TASK_SIZE is 0x80000000 on ppc32. >> >> I was wondering if anyone know why this was still the case? Seems >> like we have a 1Gb whole between TASK_SIZE & KERNELBASE. > > Two reasons: (a) PReP used to map PCI stuff with BATs in the > 0x80000000 - 0xbfffffff region, and (b) some embedded ports with > software-loaded TLBs test just the high bit of the address to > determine whether to use the kernel or user page tables. Can you explain (a) further -- I'm assuming the BAT mapping is 1:1 for that region? For (b) it looks like: * 40x, 44x, fsl-booke compare against TASK_SIZE in their software handlers. * 8xx still tests 0x80000000 * 6xx (603) compares against KERNELBASE It would seem like we should set the default on 8xx & PReP to 0x80000000 and not allow it to be modified since that will break the world and for everything else move it to match KERNELBASE. Any issues with that? - k