Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751288Ab3CRDwm (ORCPT ); Sun, 17 Mar 2013 23:52:42 -0400 Received: from mail-da0-f44.google.com ([209.85.210.44]:41314 "EHLO mail-da0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751089Ab3CRDwl (ORCPT ); Sun, 17 Mar 2013 23:52:41 -0400 Message-ID: <51468FC9.2030203@ozlabs.ru> Date: Mon, 18 Mar 2013 14:53:45 +1100 From: Alexey Kardashevskiy User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 MIME-Version: 1.0 To: Alex Williamson CC: David Gibson , Joerg Roedel , Benjamin Herrenschmidt , linux-kernel@vger.kernel.org Subject: Re: [PATCH] iommu: making IOMMU sysfs nodes API public 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> <1361334800.2801.284.camel@bling.home> In-Reply-To: <1361334800.2801.284.camel@bling.home> Content-Type: text/plain; charset=KOI8-R; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11499 Lines: 243 On 20/02/13 15:33, Alex Williamson wrote: > 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, Continuing the discussion :) In meanwhile I added/tested VFIO_IOMMU_ENABLE and VFIO_IOMMU_DISABLE like that (will repost the patch later, may be this week, only few changes there): + case VFIO_IOMMU_ENABLE: { + mutex_lock(&container->lock); + ret = tce_iommu_enable(container); + mutex_unlock(&container->lock); + + return ret; + } + case VFIO_IOMMU_DISABLE: { + mutex_lock(&container->lock); + tce_iommu_disable(container); + mutex_unlock(&container->lock); + + return 0; + } and defined them as (not arch specific): +/* IOCTLs to enable/disable IOMMU container usage */ +#define VFIO_IOMMU_ENABLE _IO(VFIO_TYPE, VFIO_BASE + 15) +#define VFIO_IOMMU_DISABLE _IO(VFIO_TYPE, VFIO_BASE + 16) should be ok, right? There is another question. It is possible to compile vfio_iommu_spapr_tce as a module. How/when is it supposed to be loaded? A user may not want to do "modprobe vfio_iommu_spapr_tce" manually. -- Alexey -- 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/