From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: qemu/hw/device-assignment: questions about msix_table_page Date: Tue, 5 May 2009 13:34:50 +0300 Message-ID: <20090505103450.GB15418@redhat.com> References: <20090427104117.GB29082@redhat.com> <200904272203.59909.sheng@linux.intel.com> <20090427141504.GC2504@redhat.com> <200904272230.18253.sheng@linux.intel.com> <20090505095136.GA12797@redhat.com> <20090505101945.GA11426@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Sheng Yang , Avi Kivity , kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from mx2.redhat.com ([66.187.237.31]:48382 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753460AbZEEKft (ORCPT ); Tue, 5 May 2009 06:35:49 -0400 Content-Disposition: inline In-Reply-To: <20090505101945.GA11426@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, May 05, 2009 at 07:19:45AM -0300, Marcelo Tosatti wrote: > On Tue, May 05, 2009 at 12:51:36PM +0300, Michael S. Tsirkin wrote: > > On Mon, Apr 27, 2009 at 10:30:17PM +0800, Sheng Yang wrote: > > > > > > > If guest can write to the real device MSI-X table directly, it would > > > > > > > cause chaos on interrupt delivery, for what guest see is totally > > > > > > > different with what's host see... > > > > > > > > > > > > Obviously. > > > > > > > > > > > > Thanks, > > > > > > > What's the reason that this page is unmapped from the qemu memory space? > > Specifically what do these lines do: > > int offset = r_dev->msix_table_addr - real_region->base_addr; > > ret = munmap(region->u.r_virtbase + offset, TARGET_PAGE_SIZE); > > I believe this allows accesses to this page (the MSI-X table), which > is part of the guest address space (through kvm memory slots), to be > trapped by qemu. > > Since there is no actual page in this guest address, KVM treats accesses > as MMIO and forwards them to QEMU. > > I thought about this too. But why is this necessary for assigned MSI-X but not for emulated devices such as e.g. e1000? All e1000 does seems to be cpu_register_physical_memory ... -- MST