Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758009AbbGGQhK (ORCPT ); Tue, 7 Jul 2015 12:37:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60591 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932198AbbGGQhE (ORCPT ); Tue, 7 Jul 2015 12:37:04 -0400 Date: Tue, 7 Jul 2015 18:36:53 +0200 From: Thomas Huth To: "Michael S. Tsirkin" Cc: Greg Kurz , Linus Torvalds , KVM list , virtualization , Network Development , Linux Kernel Mailing List , Cornelia Huck , kraxel@redhat.com Subject: Re: [PULL] virtio/vhost: cross endian support Message-ID: <20150707183653.462b5df0@thh440s> In-Reply-To: <20150702112809-mutt-send-email-mst@redhat.com> References: <20150701113150-mutt-send-email-mst@redhat.com> <20150702071412-mutt-send-email-mst@redhat.com> <20150702111256.13f8ea71@bahia.local> <20150702112809-mutt-send-email-mst@redhat.com> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2176 Lines: 59 On Thu, 2 Jul 2015 11:32:52 +0200 "Michael S. Tsirkin" wrote: > On Thu, Jul 02, 2015 at 11:12:56AM +0200, Greg Kurz wrote: > > On Thu, 2 Jul 2015 08:01:28 +0200 > > "Michael S. Tsirkin" wrote: ... > > > Yea, well - support for legacy BE guests on the new LE hosts is > > > exactly the motivation for this. > > > > > > I dislike it too, but there are two redeeming properties that > > > made me merge this: > > > > > > 1. It's a trivial amount of code: since we wrap host/guest accesses > > > anyway, almost all of it is well hidden from drivers. > > > > > > 2. Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY - > > > and when it's clear, there's zero overhead (as some point it was > > > tested by compiling with and without the patches, got the same > > > stripped binary). > > > > > > Maybe we could create a Kconfig symbol to enforce point (2): prevent > > > people from enabling it e.g. on x86. I will look into this - but it can > > > be done by a patch on top, so I think this can be merged as is. > > > > > > > This cross-endian *oddity* is targeting PowerPC book3s_64 processors... I > > am not aware of any other users. Maybe create a symbol that would > > be only selected by PPC_BOOK3S_64 ? > > I think some ARM systems are trying to support cross-endian > configurations as well. > > Besides that, yes, this is more or less what I had in mind. Would something simple like this already do the job: diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig --- a/drivers/vhost/Kconfig +++ b/drivers/vhost/Kconfig @@ -35,6 +35,7 @@ config VHOST config VHOST_CROSS_ENDIAN_LEGACY bool "Cross-endian support for vhost" + depends on KVM_BOOK3S_64 || KVM_ARM_HOST default n ---help--- This option allows vhost to support guests with a different byte ? If that looks acceptable, I can submit a proper patch if you like. Thomas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/