From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Horman Subject: Re: [PATCH]: xl: pci multi-function passthrough v2 Date: Tue, 10 Aug 2010 12:00:17 -0400 Message-ID: <20100810160017.GO3350@verge.net.au> References: <1281355239.18490.259.camel@qabil.uk.xensource.com> <20100809202703.GL17141@verge.net.au> <1281439546.18490.277.camel@qabil.uk.xensource.com> <20100810152518.GH3350@verge.net.au> <1281454278.18490.292.camel@qabil.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1281454278.18490.292.camel@qabil.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Gianni Tedesco Cc: Xen Devel , Ian Jackson , Stefano Stabellini List-Id: xen-devel@lists.xenproject.org On Tue, Aug 10, 2010 at 04:31:18PM +0100, Gianni Tedesco wrote: > On Tue, 2010-08-10 at 16:25 +0100, Simon Horman wrote: > > On Tue, Aug 10, 2010 at 12:25:46PM +0100, Gianni Tedesco wrote: > > > On Mon, 2010-08-09 at 21:27 +0100, Simon Horman wrote: > > > > On Mon, Aug 09, 2010 at 01:00:39PM +0100, Gianni Tedesco wrote: > > > > > Changes since last time: > > > > > 1. Incorporate Stefanos feedback wrt. coding style, commenting > > > > > non-obvious code and making single-function a special-case of > > > > > multi-function > > > > > 2. Also fix the case for passing through a single sub-function and > > > > > re-mapping it as a single-function virtual device. (ie: pfunc = > > > > > non-zero, vfunc = zero). Apparently needed for SR-IOV. > > > > > 3. One-liner format change in xl pci-list-assignable to make it > > > > > print a copy-and-pasteable BDF. > > > > > 8<---------------------------------------- > > > > > > > > > > Implement PCI pass-through for multi-function devices. The supported BDF > > > > > notation is: BB:DD.* - therefore passing-through a subset of functions or > > > > > remapping the function numbers is not supported except for when passing > > > > > through a single function which will be a virtual function 0. > > > > > > > > Is there any plan to extend this to allow for re-mapping and the like. > > > > When I worked on the original multi-function support (last year) > > > > this seemed to be a requirement of some people. > > > > > > I am glad you asked > > > > > > I initially planned to support this but it seemed like a nightmare: > > > 1. The BDF notation practically becomes a regex language ;) > > > > I don't think its reasonable to say it becomes a regex language. > > But I do agree that it becomes more complex. > > Well, for example BB:DD.0=7-7=0 is supposed to reverse the > assignments.... but why? :) Because 0 maps to 7, 7 maps to 0 and everything in between is implied. I don't dispute that this is complex. And actually this mapping bit really pushes the extension of the notation further than I initially envisaged. So yes, I think that it is complex. But I don't think its a regex language. > > > > 2. For HVM, if a function 0 is not passed through then you don't > > > generate an SCI interrupt for PCI hotplug. > > > > Isn't it sufficient to make sure that the guest sees a function 0, > > regardless of what the physical function number is? Or am I missing > > something? > > Yes that's all that's required. > > > > 3. I couldn't imagine a scenario where this wasn't erroneous thing to do > > > > I'm not sure that I understand this point. > > I agree that your system should always produce a valid result. > > But I think that there are other configurations that are > > both valid and useful. > > Passing various functions in to different VM's and/or re-mapping the > function numbers may produce a totally invalid configuration that isn't > useful (AFAICT). That may be paranoia but I just want to be convinced > that this is actually useful for something. Yes, I agree that the scheme that I implemented can produce invalid results. I was concerned about that too. And initially I resisted allowing arbitrary mappings for that reason. But I was convinced/requested to allow them. > > > But if someone can convince me that this is a worth-while thing to do > > > (3) then (1) and (2) are just technical problems which can be > > > overcome... > > > > People convinced me that it was worthwhile, but I'm not those people. > > Well, please put them in touch or maybe forward the relevant > discussions? (off-list is OK, if the discussions are private) > > Like I say, I am not dead against the idea, I am just loathe to > implement it until I can see what the point of it is. I think that its a wise position for you to take.