From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hollis Blanchard Subject: Re: [PATCH] [v2] linux: virtio: Standardize virtio's concept of "page size" Date: Wed, 12 Nov 2008 10:16:31 -0600 Message-ID: <1226506591.19156.10.camel@localhost.localdomain> References: <200811122251.14159.rusty@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org, markmc-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, xiantao.zhang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kvm-ppc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Rusty Russell Return-path: In-Reply-To: <200811122251.14159.rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org> Sender: kvm-ppc-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: kvm.vger.kernel.org On Wed, 2008-11-12 at 22:51 +1030, Rusty Russell wrote: > On Tuesday 11 November 2008 10:07:09 Hollis Blanchard wrote: > > Both sides of the virtio interface must agree about how big a pfn really > > is. This is particularly an issue on architectures where the page size is > > configurable (e.g. PowerPC, IA64) -- the interface must be independent of > > PAGE_SHIFT. > > > > Currently there are three distinct problems: > > * The shift count used when passing the physical address of the ring to a > > PCI-based back end. > > * The ring layout itself is padded to span at least two "pages". > > * The balloon driver operates in units of "pages". > > Hi Hollis, > > The more I thought about this, the more I think we're not solving this > as neatly as we could. The trigger was noting that we're breaking the > userspace API (vring_size and vring_init are exposed to userspace): I > know that qemu cut & pastes, but that's no excuse. > > So instead, I've introduced separate constants for each use. Yes, > all these constants are 12/4096. But just to be contrary, at the end > is a patch to change lguest to 128. And there's no reason this > couldn't change in future using some guest detection scheme. OK. I thought it was simpler to just say "4KB everywhere" in all aspects of the virtio interface, but I'm happy as long as we solve the problem somehow. :) -- Hollis Blanchard IBM Linux Technology Center -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html