From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755567Ab2BGPXW (ORCPT ); Tue, 7 Feb 2012 10:23:22 -0500 Received: from mail-pw0-f46.google.com ([209.85.160.46]:51848 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754407Ab2BGPXV (ORCPT ); Tue, 7 Feb 2012 10:23:21 -0500 Message-ID: <4F3141E4.8080902@codemonkey.ws> Date: Tue, 07 Feb 2012 09:23:16 -0600 From: Anthony Liguori User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.23) Gecko/20110922 Lightning/1.0b2 Thunderbird/3.1.15 MIME-Version: 1.0 To: Alexander Graf CC: Avi Kivity , qemu-devel , kvm-ppc , KVM list , linux-kernel Subject: Re: [Qemu-devel] [RFC] Next gen kvm api References: <4F2AB552.2070909@redhat.com> <4F2B41D6.8020603@codemonkey.ws> <51470503-DEE0-478D-8D01-020834AF6E8C@suse.de> <4F3117E5.6000105@redhat.com> <4F31241C.70404@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/07/2012 07:40 AM, Alexander Graf wrote: > > Why? For the HPET timer register for example, we could have a simple MMIO hook that says > > on_read: > return read_current_time() - shared_page.offset; > on_write: > handle_in_user_space(); > > For IDE, it would be as simple as > > register_pio_hook_ptr_r(PIO_IDE, SIZE_BYTE,&s->cmd[0]); > for (i = 1; i< 7; i++) { > register_pio_hook_ptr_r(PIO_IDE + i, SIZE_BYTE,&s->cmd[i]); > register_pio_hook_ptr_w(PIO_IDE + i, SIZE_BYTE,&s->cmd[i]); > } You can't easily serialize updates to that address with the kernel since two threads are likely going to be accessing it at the same time. That either means an expensive sync operation or a reliance on atomic instructions. But not all architectures offer non-word sized atomic instructions so it gets fairly nasty in practice. Regards, Anthony Liguori