From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934158Ab3BTEd3 (ORCPT ); Tue, 19 Feb 2013 23:33:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44895 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932790Ab3BTEd2 (ORCPT ); Tue, 19 Feb 2013 23:33:28 -0500 Message-ID: <1361334800.2801.284.camel@bling.home> Subject: Re: [PATCH] iommu: making IOMMU sysfs nodes API public From: Alex Williamson To: Alexey Kardashevskiy Cc: David Gibson , Joerg Roedel , Benjamin Herrenschmidt , linux-kernel@vger.kernel.org Date: Tue, 19 Feb 2013 21:33:20 -0700 In-Reply-To: <51244F10.3000002@ozlabs.ru> References: <1360628713.3248.8.camel@bling.home> <1360642004-7419-1-git-send-email-aik@ozlabs.ru> <1360645643.3248.91.camel@bling.home> <511A54DC.9030908@ozlabs.ru> <1360689304.3248.154.camel@bling.home> <5121C709.80007@ozlabs.ru> <1361251440.2801.142.camel@bling.home> <20130219073853.GS21067@truffula.fritz.box> <1361304711.2801.232.camel@bling.home> <51243567.5080602@ozlabs.ru> <1361332078.2801.275.camel@bling.home> <51244F10.3000002@ozlabs.ru> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-02-20 at 15:20 +1100, Alexey Kardashevskiy wrote: > On 20/02/13 14:47, Alex Williamson wrote: > > On Wed, 2013-02-20 at 13:31 +1100, Alexey Kardashevskiy wrote: > >> On 20/02/13 07:11, Alex Williamson wrote: > >>> On Tue, 2013-02-19 at 18:38 +1100, David Gibson wrote: > >>>> On Mon, Feb 18, 2013 at 10:24:00PM -0700, Alex Williamson wrote: > >>>>> On Mon, 2013-02-18 at 17:15 +1100, Alexey Kardashevskiy wrote: > >>>>>> On 13/02/13 04:15, Alex Williamson wrote: > >>>>>>> On Wed, 2013-02-13 at 01:42 +1100, Alexey Kardashevskiy wrote: > >>>>>>>> On 12/02/13 16:07, Alex Williamson wrote: > >>>>>>>>> On Tue, 2013-02-12 at 15:06 +1100, Alexey Kardashevskiy wrote: > >>>>>>>>>> Having this patch in a tree, adding new nodes in sysfs > >>>>>>>>>> for IOMMU groups is going to be easier. > >>>>>>>>>> > >>>>>>>>>> The first candidate for this change is a "dma-window-size" > >>>>>>>>>> property which tells a size of a DMA window of the specific > >>>>>>>>>> IOMMU group which can be used later for locked pages accounting. > >>>>>>>>> > >>>>>>>>> I'm still churning on this one; I'm nervous this would basically creat > >>>>>>>>> a /proc free-for-all under /sys/kernel/iommu_group/$GROUP/ where any > >>>>>>>>> iommu driver can add random attributes. That can get ugly for > >>>>>>>>> userspace. > >>>>>>>> > >>>>>>>> Is not it exactly what sysfs is for (unlike /proc)? :) > >>>>>>> > >>>>>>> Um, I hope it's a little more thought out than /proc. > >>>>>>> > >>>>>>>>> On the other hand, for the application of userspace knowing how much > >>>>>>>>> memory to lock for vfio use of a group, it's an appealing location to > >>>>>>>>> get that information. Something like libvirt would already be poking > >>>>>>>>> around here to figure out which devices to bind. Page limits need to be > >>>>>>>>> setup prior to use through vfio, so sysfs is more convenient than > >>>>>>>>> through vfio ioctls. > >>>>>>>> > >>>>>>>> True. DMA window properties do not change since boot so sysfs is the right > >>>>>>>> place to expose them. > >>>>>>>> > >>>>>>>>> But then is dma-window-size just a vfio requirement leaking over into > >>>>>>>>> iommu groups? Can we allow iommu driver based attributes without giving > >>>>>>>>> up control of the namespace? Thanks, > >>>>>>>> > >>>>>>>> Who are you asking these questions? :) > >>>>>>> > >>>>>>> Anyone, including you. Rather than dropping misc files in sysfs to > >>>>>>> describe things about the group, I think the better solution in your > >>>>>>> case might be a link from the group to an existing sysfs directory > >>>>>>> describing the PE. I believe your PE is rooted in a PCI bridge, so that > >>>>>>> presumably already has a representation in sysfs. Can the aperture size > >>>>>>> be determined from something in sysfs for that bridge already? I'm just > >>>>>>> not ready to create a grab bag of sysfs entries for a group yet. > >>>>>>> Thanks, > >>>>>> > >>>>>> > >>>>>> At the moment there is no information neither in sysfs nor > >>>>>> /proc/device-tree about the dma-window. And adding a sysfs entry per PE > >>>>>> (powerpc partitionable end-point which is often a PHB but not always) just > >>>>>> for VFIO is quite heavy. > >>>>> > >>>>> How do you learn the window size and PE extents in the host kernel? > >>>>> > >>>>>> We could add a ppc64 subfolder under /sys/kernel/iommu/xxx/ and put the > >>>>>> "dma-window" property there. And replace it with a symlink when and if we > >>>>>> add something for PE later. Would work? > >>>> > >>>> Fwiw, I'd suggest a subfolder named for the type of IOMMU, rather than > >>>> "ppc64". > >>>> > >>>>> To be clear, you're suggesting /sys/kernel/iommu_groups/$GROUP/xxx/, > >>>>> right? A subfolder really only limits the scope of the mess, so it's > >>>>> not much improvement. What does the interface look like to make those > >>>>> subfolders? > >>>>> > >>>>> The problem we're trying to solve is this call flow: > >>>>> > >>>>> containerfd = open("/dev/vfio/vfio"); > >>>>> ioctl(containerfd, VFIO_GET_API_VERSION); > >>>>> ioctl(containerfd, VFIO_CHECK_EXTENSION, ...); > >>>>> groupfd = open("/dev/vfio/$GROUP"); > >>>>> ioctl(groupfd, VFIO_GROUP_GET_STATUS); > >>>>> ioctl(groupfd, VFIO_GROUP_SET_CONTAINER, &containerfd); > >>>>> > >>>>> You wanted to lock all the memory for the DMA window here, before we can > >>>>> call VFIO_IOMMU_GET_INFO, but does it need to happen there? We still > >>>>> have a MAP_DMA hook. We could do it all on the first mapping. > >>>> > >>>> MAP_DMA isn't quite enough, since the guest can also directly cause > >>>> mappings using hypercalls directly implemented in KVM. I think it > >>>> would be feasible to lock on the first mapping (either via MAP_DMA, or > >>>> H_PUT_TCE) though it would be a bit ugly and require that the first > >>>> H_PUT_TCE always bounce out to virtual mode (Alexey, correct me if I'm > >>>> wrong here). IIRC there is also a call to bind the vfio container to > >>>> a (qemu assigned) LIOBN, before the guest can use H_PUT_TCE directly, > >>>> so that might be another place we could do the lock. > >>> > >>> Somehow hypercall mappings have to be gated by the userspace setup, > >>> right? > >> > >> > >> There is a KVM ioctl (and a KVM capability) which hooks LIOBN (PCI bus ID) > >> with IOMMU ID. It basically creates an entry in the list of all LIOBNs and > >> when TCE call occurs, the host finds correct IOMMU group to pass this call to. > >> > >> It happens from spapr_register_vfio_container() in QEMU, i.e. after getting > >> DMA window properties but only if the host supports real mode TCE handling. > >> > >> > >>>>> It also > >>>>> has a flags field that could augment the behavior to trigger page > >>>>> locking. > >>>> > >>>> I don't see how the flags help us - we can't have userspace choose to > >>>> skip the locked memory accounting. Or are you suggesting a flag to > >>>> open the container in some sort of dummy mode where only GET_INFO is > >>>> possible, then re-open with the full locking? > >>> > >>> Sort of, I don't think it needs to be re-opened, but we had previously > >>> talked about some kind of enable and disable ioctl. "enable" would be > >>> the logical place to lock pages, but then we probably got stuck in > >>> questions around what it means to enable an iommu generically. > >> > >> The other question is if a container is ready to work if I add just one > >> group? What happens when I add another one (not supported on ppc64 but > >> still)? > > > > This is also the problem with exposing a dma window under the group in > > sysfs. Do I require the ability to lock the sum of the window, the > > largest window, what? If we rely on the ioctls, userspace can figure > > out that they can't be combined and know it's the sum. I'm not sure > > what your plans are around hotplug of a PHB though. > > > >> Having "enable" method and disabling new attachments when it is > >> "enabled" would keep my brain calm :) > > > > Now I'm not sure whether you're for or against it ;) > > > I am for introducing enable() ioctls :) Or even "lock" ioctl. > > > >>> So what > >>> if instead of a separate enable ioctl we had a flag on DMA_MAP that was > >>> defined as SET_WINDOW where iova and size are passed and specify the > >>> portion of the DMA window that userspace intends to use and which is > >>> therefore locked. If you don't support subwindows, fine, just fail it. > >>> You could have a matching PUT_WINDOW on DMA_UNMAP if you wanted. > >> > >> DMA_MAP which does not do "map" but does "lock" or "set window"? > >> enable()/disable() look better. > > > > Sure, this is why we have a modular iommu interface, spapr can create an > > enable ioctl if necessary. I think there are ways to use the > > DMA_MAP/UNMAP ioctl in ways that aren't a complete kludge though. > > > >>>>> Adding the window size to sysfs seems more readily convenient, > >>>>> but is it so hard for userspace to open the files and call a couple > >>>>> ioctls to get far enough to call IOMMU_GET_INFO? I'm unconvinced the > >>>>> clutter in sysfs more than just a quick fix. Thanks, > >>>> > >>>> And finally, as Alexey points out, isn't the point here so we know how > >>>> much rlimit to give qemu? Using ioctls we'd need a special tool just > >>>> to check the dma window sizes, which seems a bit hideous. > >>> > >>> Is it more hideous that using iommu groups to report a vfio imposed > >>> restriction? Are a couple open files and a handful of ioctls worse than > >>> code to parse directory entries and the future maintenance of an > >>> unrestricted grab bag of sysfs entries? > >> > >> At the moment DMA32 window properties are static. So I can easily get rid > >> of VFIO_IOMMU_SPAPR_TCE_GET_INFO and be happy. > > > > Like, for instance, every PE always gets 512MB DMA window, fixed base > > address, not configurable, end of story? > > > Almost :) 1GB, starting at 0 (sometime at 2GB). Multiple PCI domains are > supported on ppc64 so it does not make a problem as bus address spaces are > separated. But yes, not flexible at all. Statements like "at the moment...", "[but] sometimes at..." make me think it's best to keep the GET_INFO call. > >> Ah, anyway, how do you see these ioctls to work on a user machine? > >> A separate tool which takes an iommu id, returns DMA window size and > >> adjusts rlimit? > > > > Sure, we need something that provides the function of libvirt and > > unbinds devices from host drivers, re-binds them to vfio-pci. That tool > > needs to have permissions to manipulate groups, so we're just talking > > about whether it's stepping over the line for it to open the group and a > > container, associate them, and probe the iommu info vs reading a sysfs > > file. Thanks, > > So the Tool is going to be a part of libvirt but not kernel or qemu, right? > Then implementing "LOCK" (and call it after GET_INFO in QEMU and not call > it from the Tool) should work fine. Right, a probe tool would check the value, close the files and set the locked page limit for qemu, which would take the next step to trigger the in-kernel accounting. Thanks, Alex