From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 2/3] KVM: Emulate MSI-X table in kernel Date: Mon, 17 Jan 2011 14:18:43 +0200 Message-ID: <4D3433A3.2010305@redhat.com> References: <1294309185-21417-1-git-send-email-sheng@linux.intel.com> <1294309185-21417-3-git-send-email-sheng@linux.intel.com> <20110117115447.GA8145@amt.cnet> <201101172018.22478.sheng@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , "Michael S. Tsirkin" , kvm@vger.kernel.org To: Sheng Yang Return-path: Received: from mx1.redhat.com ([209.132.183.28]:58958 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750945Ab1AQMSr (ORCPT ); Mon, 17 Jan 2011 07:18:47 -0500 In-Reply-To: <201101172018.22478.sheng@linux.intel.com> Sender: kvm-owner@vger.kernel.org List-ID: On 01/17/2011 02:18 PM, Sheng Yang wrote: > > > + > > > + if (copy_to_user((void __user *)(entry_base + offset), val, len)) > > > + goto out; > > > > Instead of copying to/from userspace (which is subject to swapin, > > unexpected values), you could include the guest written value in a > > kvm_run structure, along with address. Qemu-kvm would use that to > > synchronize its copy of the table, on KVM_EXIT_MSIX_ROUTING_UPDATE exit. > > We want to acelerate MSI-X mask bit accessing, which won't exit to userspace in > the most condition. That's the cost we want to optimize. Also it's possible to > userspace to read the correct value of MMIO(but mostly userspace can't write to it > in order to prevent synchronize issue). It's also good to have the values in just one place; using userspace makes it easy for both the kernel and userspace to see the values (and set them after migration, if/when we extend this to virtio). -- error compiling committee.c: too many arguments to function