From owner-freebsd-hackers@FreeBSD.ORG Mon Apr 21 06:22:52 2003 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 651ED37B401 for ; Mon, 21 Apr 2003 06:22:52 -0700 (PDT) Received: from k6.locore.ca (k6.locore.ca [198.96.117.170]) by mx1.FreeBSD.org (Postfix) with ESMTP id 02BCD43FDD for ; Mon, 21 Apr 2003 06:22:51 -0700 (PDT) (envelope-from jake@k6.locore.ca) Received: from k6.locore.ca (localhost.locore.ca [127.0.0.1]) by k6.locore.ca (8.12.8/8.12.8) with ESMTP id h3LDOpxS052610; Mon, 21 Apr 2003 09:24:51 -0400 (EDT) (envelope-from jake@k6.locore.ca) Received: (from jake@localhost) by k6.locore.ca (8.12.8/8.12.8/Submit) id h3LDOooQ052609; Mon, 21 Apr 2003 09:24:50 -0400 (EDT) Date: Mon, 21 Apr 2003 09:24:49 -0400 From: Jake Burkholder To: Marcel Moolenaar Message-ID: <20030421132449.GA50754@locore.ca> References: <20030421055332.GA4680@dhcp01.pn.xcllnt.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030421055332.GA4680@dhcp01.pn.xcllnt.net> User-Agent: Mutt/1.4i cc: freebsd-hackers@freebsd.org Subject: Re: Is pmap_kextract() allowed to fault? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Apr 2003 13:22:52 -0000 Apparently, On Sun, Apr 20, 2003 at 10:53:32PM -0700, Marcel Moolenaar said words to the effect of; > Gang, > > On ia64 pmap_kextract() uses the tpa instruction which given a > virtual address returns the physical address based on the > translation registers and cache (ie TLB). This can fault when > there's currently no mapping for the virtual address. > > Since all other architectures have a non-faulting implementation > (AFAICT), I'm a bit worried that we might get into trouble on > ia64. I couldn't find anything about pmap_kextract(), so maybe > anybody can enlighten me: > > 1. Is pmap_kextract() allowed to fault? It depends what kind of fault. Will tpa fail if it causes a tlb fault and the page is not in the vhpt (or whatever the fault handler searches), or will it end up calling vm_fault and actually trying to fault in the page? pmap_extract/pmap_kextract are supposed to fail if the page is not mapped by the pmap. > 2. Is pmap_kextract() used often enough that using the cpu's TLB > is a possible performance speedup even if there are costly faults > that can sometimes happen? I doubt it. Jake