From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e28smtp09.in.ibm.com (e28smtp09.in.ibm.com [122.248.162.9]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e28smtp09.in.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id C96E82C0291 for ; Thu, 14 Feb 2013 01:26:52 +1100 (EST) Received: from /spool/local by e28smtp09.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 13 Feb 2013 19:55:06 +0530 Received: from d28relay01.in.ibm.com (d28relay01.in.ibm.com [9.184.220.58]) by d28dlp01.in.ibm.com (Postfix) with ESMTP id 1FCF4E0050 for ; Wed, 13 Feb 2013 19:57:37 +0530 (IST) Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay01.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r1DEQga123658572 for ; Wed, 13 Feb 2013 19:56:42 +0530 Received: from d28av05.in.ibm.com (loopback [127.0.0.1]) by d28av05.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r1DEQi45014189 for ; Thu, 14 Feb 2013 01:26:45 +1100 From: "Aneesh Kumar K.V" To: David Laight , Benjamin Herrenschmidt , phileas-fogg@mail.ru, geoff@infradead.org Subject: RE: [PATCH 2/2] powerpc: Make context bits depend on virtual addr size. In-Reply-To: References: <1360693905-23503-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1360693905-23503-2-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1360701185.2035.10.camel@pasglop> <87sj50kian.fsf@linux.vnet.ibm.com> <1360727211.2035.30.camel@pasglop> <87pq04jvb4.fsf@linux.vnet.ibm.com> Date: Wed, 13 Feb 2013 19:56:44 +0530 Message-ID: <87mwv8jnmj.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain Cc: paulus@samba.org, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , David Laight writes: >> +#define CONTEXT_BITS 19 >> +#define USER_ESID_BITS 18 >> +#define USER_ESID_BITS_1T 6 >> + >> +/* >> + * 256MB segment >> + * The proto-VSID space has 2^(CONTEX_BITS + USER_ESID_BITS) - 1 segments >> + * available for user + kernel mapping. The top 4 contexts are used for >> + * kernel mapping. Each segment contains 2^28 bytes. Each >> + * context maps 2^46 bytes (64TB) so we can support 2^19-1 contexts >> + * (19 == 37 + 28 - 46). >> + */ > > I can't help feeling this would be easier to understand if a full > 64? 80? bit address was shown with the various bit ranges identified. > > Given the comment, I'd have expected CONTEXT_BITS to be calculated > from three other named constants - rather than being set to 19. > May be the comments were misleading. We build proto vsid using a combination of context and ea bits. Current code does the below: for kernel: proto_vsid = ea >> SID_SHIFT; proto_vsid |= (1UL << (CONTEXT_BITS + USER_ESID_BITS)); for user: proto_vsid = ea >> SID_SHIFT proto_vsid |= context << USER_ESID_BITS context range is 0 - (2^19 -1) With this patch we _don't_ give kernel half the proto vsid range. Instead, we reduce the proto vsid range and then the kernel is given top 4 context. ie, kernel proto vsid is now for kenel: proto_vsid = ea >> SID_SHIFT; context = (MAX_CONTEXT - 4) + ((effective address >> 60) - 0xc); proto_vsid |= context << USER_ESID_BITS -aneesh