From owner-freebsd-current@FreeBSD.ORG Sun Oct 5 11:23:55 2014 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 82E64D18; Sun, 5 Oct 2014 11:23:55 +0000 (UTC) Received: from smtp.mei.co.jp (smtp.mei.co.jp [133.183.100.20]) by mx1.freebsd.org (Postfix) with ESMTP id 0B908A89; Sun, 5 Oct 2014 11:23:54 +0000 (UTC) Received: from mail-gw.jp.panasonic.com ([157.8.1.157]) by smtp.mei.co.jp (8.12.11.20060614/3.7W/kc-maile12) with ESMTP id s95BNlAB018986; Sun, 5 Oct 2014 20:23:47 +0900 (JST) Received: from epochmail.jp.panasonic.com ([157.8.1.130]) by mail.jp.panasonic.com (8.11.6p2/3.7W/kc-maili11) with ESMTP id s95BNlR10517; Sun, 5 Oct 2014 20:23:47 +0900 Received: by epochmail.jp.panasonic.com (8.12.11.20060308/3.7W/lomi14) id s95BNlpQ029678; Sun, 5 Oct 2014 20:23:47 +0900 Received: from localhost by lomi14.jp.panasonic.com (8.12.11.20060308/3.7W) with ESMTP id s95BNlp4029658; Sun, 5 Oct 2014 20:23:47 +0900 Date: Sun, 05 Oct 2014 20:23:47 +0900 (JST) Message-Id: <20141005.202347.1457045051130679424.okuno.kohji@jp.panasonic.com> To: kostikbel@gmail.com Subject: Re: About pmap_mapdev() & pmap_unmapdev() From: Kohji Okuno In-Reply-To: <20141005085753.GX26076@kib.kiev.ua> References: <20141004155803.GQ26076@kib.kiev.ua> <20141005.131512.606074419488263735.okuno.kohji@jp.panasonic.com> <20141005085753.GX26076@kib.kiev.ua> Organization: Panasonic Corporation X-Mailer: Mew version 6.5 on Emacs 24.3 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: stable@freebsd.org, freebsd-current@freebsd.org, okuno.kohji@jp.panasonic.com X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 05 Oct 2014 11:23:55 -0000 Hi Konstantin, Thank you very much for your detailed explanatin. I understood the policy of vmem. Many thanks, Kohji Okuno > On Sun, Oct 05, 2014 at 01:15:12PM +0900, Kohji Okuno wrote: >> Hi, >> >> > On Sat, Oct 04, 2014 at 08:53:35PM +0900, Kohji Okuno wrote: >> >> Hi Konstantin, >> >> >> >> Thank you for your prompt response. >> >> I will test and report from next monday. >> >> >> >> >> In addtion, I have one question. >> >> >> In current and 10-stable, is vm_map_delete() called by kva_free()? >> >> > No, kva_free() only releases the vmem backing, leaving the page >> >> > tables intact. This is why I only did the stable/9 patch. >> >> >> >> Where are PTEs allocated by pmap_mapdev() freed in current and 10-stable? >> >> Could you please explain me? >> > They are not freed. The removal of the vmem which covers the address >> > space managed by corresponding ptes, allows the reuse of both KVA region >> > and corresponding PTEs in the tables. The only concern with the resident >> > page tables is to avoid two kva_alloc() to step over each other, and >> > this is ensured by vmem. >> >> I agree that normal pages are reusable. But, since the pages mapped by >> pmap_mapdev() are concerned with the physicall address of device (For >> example: video memory), these PTEs aren't reusable, I think. >> So, should we free these PTEs by pmap_unmapdev()? > There is no hold on any physical pages which were referenced by the ptes. > The only thing which is left out are the records in the page tables > which map the KVA to said device memory. It is harmless. > > When the KVA is reused, the ptes in page tables are overwritten. > > It might be argued that clearing PTEs, or at least removing the PG_V > bit catches erronous unintended accesses to the freed range, but by the > cost of the overhead of re-polluting the caches. And since clearing is > not effective without doing TLB flush, which requires broadcast IPI, > it is more trouble than advantage. > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"