Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755395AbaDGRLx (ORCPT ); Mon, 7 Apr 2014 13:11:53 -0400 Received: from smtp.citrix.com ([66.165.176.89]:34785 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753190AbaDGRLu (ORCPT ); Mon, 7 Apr 2014 13:11:50 -0400 X-IronPort-AV: E=Sophos;i="4.97,811,1389744000"; d="scan'208";a="118761079" Message-ID: <5342DC54.2070608@citrix.com> Date: Mon, 7 Apr 2014 18:11:48 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20121215 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: =?UTF-8?B?Um9nZXIgUGF1IE1vbm7DqQ==?= CC: , , Konrad Rzeszutek Wilk , Boris Ostrovsky Subject: Re: [PATCH] xen-blkback: only attach blkback if the required features are met References: <1396622471-13114-1-git-send-email-roger.pau@citrix.com> <533EC966.7030101@citrix.com> <533ECC32.5070302@citrix.com> In-Reply-To: <533ECC32.5070302@citrix.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.80.2.76] X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/04/14 16:13, Roger Pau Monné wrote: > On 04/04/14 17:01, David Vrabel wrote: >> On 04/04/14 15:41, Roger Pau Monne wrote: >>> Blkback cannot work properly on auto-translated guests if Xen doesn't >>> update the IOMMU when performing grant maps/unmaps, so only attach if >>> the newly introduced XENFEAT_hvm_gntmap_supports_iommu is found. >> >> Can you explain the problem in more detail and which guest >> configurations are affected? >> >> This isn't a problem that is specific to blkback, but any backend that >> grant maps and passes the foreign pages to a device so there needs to be >> a generic solution. >> >> Why can't this be fixed by having the swiotlb bounce foreign pages? > > Yes, it could be fixed with that, FreeBSD has been doing it for a long time. > > But since nobody has complained about this, and the issue has been there > for a long time, I'm not sure it's worth adding all the bounce buffer > code for what seems to be an unused configuration. Ok. Now that netback also grant maps. Can you make this a generic function and call from netback and blkback? David -- 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/