From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerd Hoffmann Subject: Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO Date: Fri, 12 Dec 2008 21:25:58 +0100 Message-ID: <4942C8D6.5080209@redhat.com> References: <4942B841.6010900@codemonkey.ws> <20081212193743.GC30537@random.random> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , qemu-devel@nongnu.org, kvm@vger.kernel.org, avi@redhat.com, chrisw@redhat.com To: Andrea Arcangeli Return-path: Received: from mx2.redhat.com ([66.187.237.31]:43433 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751558AbYLLU0P (ORCPT ); Fri, 12 Dec 2008 15:26:15 -0500 In-Reply-To: <20081212193743.GC30537@random.random> Sender: kvm-owner@vger.kernel.org List-ID: Andrea Arcangeli wrote: > On Fri, Dec 12, 2008 at 01:15:13PM -0600, Anthony Liguori wrote: >> 1) You attempt to map a physical address. This effectively is a lock or >> pin operation. > > lock or pin for what? There's nothing to pin or lock here. Oh, there is in Xen context (i.e. qemu in dom0 handles device emulation for xen domU guests). You can ask Xen to map the grant (or guest pfn) here. I think doing so will kill the need for the mapcache patches xensource carries in the xenified qemu tree. >> 4) You unmap or unlock that memory region. The virtual address is now no >> longer valid. > > Again not needed. Likewise useful for Xen. cheers, Gerd