From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH 12/22] virtio_pci: allow duplicate capabilities. Date: Thu, 21 Mar 2013 07:45:57 -0700 Message-ID: <514B1D25.9090206@zytor.com> References: <1363854584-25795-1-git-send-email-rusty@rustcorp.com.au> <1363854584-25795-13-git-send-email-rusty@rustcorp.com.au> <20130321102814.GC30493@redhat.com> <514B188A.3030502@zytor.com> <20130321144330.GA1454@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130321144330.GA1454@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On 03/21/2013 07:43 AM, Michael S. Tsirkin wrote: >> >> The reason to support this is that a guest written to only handle one or >> the other doesn't prevent the hypervisor from offering the other to >> guests. We probably want to specify that if the guest doesn't care, it >> should use the first one offered by the host. >> > > What are the configurations where having many ways is helpful? > Any examples? > In BIOS (e.g. SeaBIOS), using MMIO is very difficult, so your boot ROM probably wants to use I/O space even if MMIO is available. If you are preferring I/O space because it is faster (vmexit), then you still want to allow MMIO if the resource is not available. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.