From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hollis Blanchard Subject: Re: [kvm-ppc-devel] RFC: MMIO endianness flag Date: Tue, 15 Jan 2008 10:22:40 -0600 Message-ID: <1200414160.9142.1.camel@basalt> References: <1199920008.5637.48.camel@basalt> <4785C199.9040002@qumranet.com> <1199978634.20324.10.camel@basalt> <4786398C.2090308@qumranet.com> <1200005864.23377.55.camel@basalt> <4789DD0C.4010600@qumranet.com> <1200329510.29077.11.camel@basalt> <478B9C41.80105@qumranet.com> <1200343421.29077.78.camel@basalt> <478CC9EF.9020907@qumranet.com> Reply-To: Hollis Blanchard Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-ppc-devel , kvm-devel To: Avi Kivity Return-path: In-Reply-To: <478CC9EF.9020907-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Tue, 2008-01-15 at 16:57 +0200, Avi Kivity wrote: > Hollis Blanchard wrote: > >> btw, isn't passthrough better handled through the tlb? i.e. actually > >> let the guest access the specially-configured memory? You can have qemu > >> mmap /dev/mem and install it as a memslot, and things should work, no? > >> (well, you might need to set some cachablility flag or other). > >> > > > > Hmm, yes you're right. Of course, qemu offers greater flexibility than > > MMUs (which are limited to page-sized granularity, for example), so it > > might still be useful to have qemu intercede. > > > > > > With the endian-aware instructions that doesn't matter, since you set > the endianness on a per-instruction granularity. And with guest tlb > controlled endianness, surely you get page granularity as well? > > > > Since we're defining a stable ABI, I'd rather have the information > > present than miss it in the future... > > So now the question is, do we see the need for qemu to intercept writes > to pass-through devices? IMO the answer is no. If it doesn't > understand anything about the device, it would be better off doing a > real pass through. If it does understand the device, it should know > which endianness it likes. OK, I'm willing to go along with this, and hope that we don't run into another use case for an endianness flag in the future. -- Hollis Blanchard IBM Linux Technology Center ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/