From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 12/22] virtio_pci: allow duplicate capabilities. Date: Thu, 21 Mar 2013 16:43:30 +0200 Message-ID: <20130321144330.GA1454@redhat.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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <514B188A.3030502@zytor.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: "H. Peter Anvin" Cc: virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Thu, Mar 21, 2013 at 07:26:18AM -0700, H. Peter Anvin wrote: > On 03/21/2013 03:28 AM, Michael S. Tsirkin wrote: > > On Thu, Mar 21, 2013 at 06:59:33PM +1030, Rusty Russell wrote: > >> Another HPA suggestion: that the device be allowed to offer duplicate > >> capabilities, particularly so it can offer a mem and an I/O bar and let > >> the guest decide (Linux guest probably doesn't care?). > >> > >> Cc: H. Peter Anvin > >> Signed-off-by: Rusty Russell > > > > I think guests is exactly the wrong place to decide, > > it really does not know whether it's running on a > > hypervisor with fast IO or fast memory. > > Also, as long as we have an IO BAR, we have problems allocating it. > > So I think we don't need this, see my suggestion > > about fixed IO addresses instead. > > > > 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. > > -hpa What are the configurations where having many ways is helpful? Any examples?