From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCHv1 0/2] xen/grant-table: fix PV guests and remove V2 support Date: Fri, 4 Jul 2014 13:21:02 +0100 Message-ID: <53B69C2E.2090903@citrix.com> References: <1404296729-23606-1-git-send-email-david.vrabel@citrix.com> <9AAE0902D5BC7E449B7C8E4E778ABCD03CB9C3@AMSPEX01CL01.citrite.net> <53B6962C.4080805@citrix.com> <9AAE0902D5BC7E449B7C8E4E778ABCD03CD12A@AMSPEX01CL01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1X32UF-0001L5-3E for xen-devel@lists.xenproject.org; Fri, 04 Jul 2014 12:21:07 +0000 In-Reply-To: <9AAE0902D5BC7E449B7C8E4E778ABCD03CD12A@AMSPEX01CL01.citrite.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Paul Durrant , David Vrabel , "xen-devel@lists.xenproject.org" Cc: Boris Ostrovsky List-Id: xen-devel@lists.xenproject.org On 04/07/14 13:01, Paul Durrant wrote: >> -----Original Message----- >> From: David Vrabel >> Sent: 04 July 2014 12:55 >> To: Paul Durrant; xen-devel@lists.xenproject.org >> Cc: Boris Ostrovsky >> Subject: Re: [Xen-devel] [PATCHv1 0/2] xen/grant-table: fix PV guests and >> remove V2 support >> >> On 04/07/14 11:59, Paul Durrant wrote: >>>> -----Original Message----- >>>> From: xen-devel-bounces@lists.xen.org [mailto:xen-devel- >>>> bounces@lists.xen.org] On Behalf Of David Vrabel >>>> Sent: 02 July 2014 11:25 >>>> To: xen-devel@lists.xenproject.org >>>> Cc: Boris Ostrovsky; David Vrabel >>>> Subject: [Xen-devel] [PATCHv1 0/2] xen/grant-table: fix PV guests and >>>> remove V2 support >>>> >>>> The first patch fixes a logn standing issue where the map/unmap of >>>> grant table frames by PV guests was unsafe and could BUG() or have >>>> other bad behaviour. This was caused by calling function that were >>>> not permitted from atomic contexts. >>>> >>>> The second patch removes all V2 table code since it is unused. >>>> >>> >>> How confident are you of that assertion? >> >> This is removing the /Linux/ code which has been using V1 only for a >> while now. >> > > If you believe that the API is likely to wither then that seems > reasonable. I would have thought the code was unlikely to see much > change though and it seems a shame to remove an interface to something > that it still there in Xen... I guess *someone* may want to use it in > future; particularly the copy-only grants could be useful for something > like IDC (if the backend was unprivileged). It's already withering. For example PVH doesn't support V2 as it doesn't handle mapping/populating the status frames. And fixing a long standing bug (see patch 1/2) was made more complicated by having to fix up the (unused) code for dealing with the status frames. And as an aside, I'm not convinced that copy-only grants are what's needed for IDC with untrusted backend. I think revocable grants are required for efficient usage of shared rings. David