On Tue, Jan 28, 2014 at 11:32:41AM +1100, Benjamin Herrenschmidt wrote: > On Thu, 2014-01-23 at 20:11 -0800, Victor Kamensky wrote: > > > I would take 50 byteswaps with a clear ABI any day over an obscure > > > standard that can avoid a single hardware-on-register instruction. > > This > > > is about designing a clean software interface, not about building an > > > optimized integrated stack. > > > > > > Unfortunately, this is going nowhere, so I think we need to stop > > this > > > thread. As you can see I have sent a patch as a clarification to > > the > > > ABI, if it's merged we can move on with more important tasks. > > > > OK, that is fine. I still believe is not the best choice, > > but I agree that we need to move on. I will respin my > > V7 KVM BE patches according to this new semantics, I will > > integrate comments that you (thanks!) and others gave me > > over mailing list and post my series again when it is ready. > > Right, the whole "host endian" is a horrible choice from every way you > look at it, but I'm afraid it's unfixable since it's already ABI :-( > Why is it a horrible choice? I don't think it's actually ABI at this point, it's undefined. The only thing fixed is PPC BE host and ARM LE host, and in both cases we currently perform a byteswap in KVM if the guest is a different endianness. Honestly I don't care which way it's defined, as long as it's defined somehow, and I have not yet seen anyone formulate how the ABI specification should be worded, so people clearly understand what's going on. If you take a look at the v2 patch "KVM: Specify byte order for KVM_EXIT_MMIO", that's where it ended up. If you can formulate something with your experience in endianness that makes this clear, it would be extremely helpful. -Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
