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 7BF0C67BE5 for ; Wed, 9 Aug 2006 22:35:34 +1000 (EST) Subject: Re: [PATCH] SLB shadow buffer From: Benjamin Herrenschmidt To: Christoph Hellwig In-Reply-To: <20060805124544.GB23494@lst.de> References: <20060804055323.1A9BE679FB@ozlabs.org> <20060805124544.GB23494@lst.de> Content-Type: text/plain Date: Wed, 09 Aug 2006 13:22:59 +0200 Message-Id: <1155122580.4040.96.camel@localhost.localdomain> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, Michael Neuling , paulus@samba.org, anton@samba.org, sfr@canb.auug.org.au List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, 2006-08-05 at 14:45 +0200, Christoph Hellwig wrote: > On Fri, Aug 04, 2006 at 03:53:19PM +1000, Michael Neuling wrote: > > This adds a shadow buffer for the SLBs and regsiters it with PHYP. > > Only the bolted SLB entries (first 3) are saved. > > What is a SLB shadow buffer and why do we need it? (I don't want to > question the patch but rather learn a little more about lowlevel ppc64 > mmu details) Yeah, same question :) I don't have my PAPR at hand and I'm still travellling but I'm curious about that one... I would suspect it allows the HV to save/restore SLBs when sharing a processor between partitions but then... the kernel requires that anyway so either the current code is bogus and that's pretty bad (which I don't think so) or maybe the fact that we didn't register the shadow caused HV to always save/restore the entire SLB, while by using the shadow, we let it save/restore only the bolted entries we put in there (and just re-fault the other ones). If it's not that, then what ? :) Ben.