On 18/08/16 10:22, Alexey Kardashevskiy wrote: > On 17/08/16 13:17, David Gibson wrote: >> On Fri, Aug 12, 2016 at 09:22:01AM -0600, Alex Williamson wrote: >>> On Fri, 12 Aug 2016 15:46:01 +1000 >>> David Gibson <da...@gibson.dropbear.id.au> wrote: >>> >>>> On Wed, Aug 10, 2016 at 10:46:30AM -0600, Alex Williamson wrote: >>>>> On Wed, 10 Aug 2016 15:37:17 +1000 >>>>> Alexey Kardashevskiy <a...@ozlabs.ru> wrote: >>>>> >>>>>> On 09/08/16 22:16, Alex Williamson wrote: >>>>>>> On Tue, 9 Aug 2016 15:19:39 +1000 >>>>>>> Alexey Kardashevskiy <a...@ozlabs.ru> wrote: >>>>>>> >>>>>>>> On 09/08/16 02:43, Alex Williamson wrote: >>>>>>>>> On Wed, 3 Aug 2016 18:40:55 +1000 >>>>>>>>> Alexey Kardashevskiy <a...@ozlabs.ru> wrote: >>>>>>>>> >>>>>>>>>> This exports helpers which are needed to keep a VFIO container in >>>>>>>>>> memory while there are external users such as KVM. >>>>>>>>>> >>>>>>>>>> Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> >>>>>>>>>> --- >>>>>>>>>> drivers/vfio/vfio.c | 30 >>>>>>>>>> ++++++++++++++++++++++++++++++ >>>>>>>>>> drivers/vfio/vfio_iommu_spapr_tce.c | 16 +++++++++++++++- >>>>>>>>>> include/linux/vfio.h | 6 ++++++ >>>>>>>>>> 3 files changed, 51 insertions(+), 1 deletion(-) >>>>>>>>>> >>>>>>>>>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c >>>>>>>>>> index d1d70e0..baf6a9c 100644 >>>>>>>>>> --- a/drivers/vfio/vfio.c >>>>>>>>>> +++ b/drivers/vfio/vfio.c >>>>>>>>>> @@ -1729,6 +1729,36 @@ long vfio_external_check_extension(struct >>>>>>>>>> vfio_group *group, unsigned long arg) >>>>>>>>>> EXPORT_SYMBOL_GPL(vfio_external_check_extension); >>>>>>>>>> >>>>>>>>>> /** >>>>>>>>>> + * External user API for containers, exported by symbols to be >>>>>>>>>> linked >>>>>>>>>> + * dynamically. >>>>>>>>>> + * >>>>>>>>>> + */ >>>>>>>>>> +struct vfio_container *vfio_container_get_ext(struct file *filep) >>>>>>>>>> +{ >>>>>>>>>> + struct vfio_container *container = filep->private_data; >>>>>>>>>> + >>>>>>>>>> + if (filep->f_op != &vfio_fops) >>>>>>>>>> + return ERR_PTR(-EINVAL); >>>>>>>>>> + >>>>>>>>>> + vfio_container_get(container); >>>>>>>>>> + >>>>>>>>>> + return container; >>>>>>>>>> +} >>>>>>>>>> +EXPORT_SYMBOL_GPL(vfio_container_get_ext); >>>>>>>>>> + >>>>>>>>>> +void vfio_container_put_ext(struct vfio_container *container) >>>>>>>>>> +{ >>>>>>>>>> + vfio_container_put(container); >>>>>>>>>> +} >>>>>>>>>> +EXPORT_SYMBOL_GPL(vfio_container_put_ext); >>>>>>>>>> + >>>>>>>>>> +void *vfio_container_get_iommu_data_ext(struct vfio_container >>>>>>>>>> *container) >>>>>>>>>> +{ >>>>>>>>>> + return container->iommu_data; >>>>>>>>>> +} >>>>>>>>>> +EXPORT_SYMBOL_GPL(vfio_container_get_iommu_data_ext); >>>>>>>>>> + >>>>>>>>>> +/** >>>>>>>>>> * Sub-module support >>>>>>>>>> */ >>>>>>>>>> /* >>>>>>>>>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c >>>>>>>>>> b/drivers/vfio/vfio_iommu_spapr_tce.c >>>>>>>>>> index 3594ad3..fceea3d 100644 >>>>>>>>>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c >>>>>>>>>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c >>>>>>>>>> @@ -1331,6 +1331,21 @@ const struct vfio_iommu_driver_ops >>>>>>>>>> tce_iommu_driver_ops = { >>>>>>>>>> .detach_group = tce_iommu_detach_group, >>>>>>>>>> }; >>>>>>>>>> >>>>>>>>>> +struct iommu_table *vfio_container_spapr_tce_table_get_ext(void >>>>>>>>>> *iommu_data, >>>>>>>>>> + u64 offset) >>>>>>>>>> +{ >>>>>>>>>> + struct tce_container *container = iommu_data; >>>>>>>>>> + struct iommu_table *tbl = NULL; >>>>>>>>>> + >>>>>>>>>> + if (tce_iommu_find_table(container, offset, &tbl) < 0) >>>>>>>>>> + return NULL; >>>>>>>>>> + >>>>>>>>>> + iommu_table_get(tbl); >>>>>>>>>> + >>>>>>>>>> + return tbl; >>>>>>>>>> +} >>>>>>>>>> +EXPORT_SYMBOL_GPL(vfio_container_spapr_tce_table_get_ext); >>>>>>>>>> + >>>>>>>>>> static int __init tce_iommu_init(void) >>>>>>>>>> { >>>>>>>>>> return vfio_register_iommu_driver(&tce_iommu_driver_ops); >>>>>>>>>> @@ -1348,4 +1363,3 @@ MODULE_VERSION(DRIVER_VERSION); >>>>>>>>>> MODULE_LICENSE("GPL v2"); >>>>>>>>>> MODULE_AUTHOR(DRIVER_AUTHOR); >>>>>>>>>> MODULE_DESCRIPTION(DRIVER_DESC); >>>>>>>>>> - >>>>>>>>>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h >>>>>>>>>> index 0ecae0b..1c2138a 100644 >>>>>>>>>> --- a/include/linux/vfio.h >>>>>>>>>> +++ b/include/linux/vfio.h >>>>>>>>>> @@ -91,6 +91,12 @@ extern void vfio_group_put_external_user(struct >>>>>>>>>> vfio_group *group); >>>>>>>>>> extern int vfio_external_user_iommu_id(struct vfio_group *group); >>>>>>>>>> extern long vfio_external_check_extension(struct vfio_group *group, >>>>>>>>>> unsigned long arg); >>>>>>>>>> +extern struct vfio_container *vfio_container_get_ext(struct file >>>>>>>>>> *filep); >>>>>>>>>> +extern void vfio_container_put_ext(struct vfio_container >>>>>>>>>> *container); >>>>>>>>>> +extern void *vfio_container_get_iommu_data_ext( >>>>>>>>>> + struct vfio_container *container); >>>>>>>>>> +extern struct iommu_table *vfio_container_spapr_tce_table_get_ext( >>>>>>>>>> + void *iommu_data, u64 offset); >>>>>>>>>> >>>>>>>>>> /* >>>>>>>>>> * Sub-module helpers >>>>>>>>> >>>>>>>>> >>>>>>>>> I think you need to take a closer look of the lifecycle of a >>>>>>>>> container, >>>>>>>>> having a reference means the container itself won't go away, but only >>>>>>>>> having a group set within that container holds the actual IOMMU >>>>>>>>> references. container->iommu_data is going to be NULL once the >>>>>>>>> groups are lost. Thanks, >>>>>>>> >>>>>>>> >>>>>>>> Container owns the iommu tables and this is what I care about here, >>>>>>>> groups >>>>>>>> attached or not - this is handled separately via IOMMU group list in a >>>>>>>> specific iommu_table struct, these groups get detached from iommu_table >>>>>>>> when they are removed from a container. >>>>>>> >>>>>>> The container doesn't own anything, the container is privileged by the >>>>>>> groups being attached to it. When groups are closed, they detach from >>>>>>> the container and once the container group list is empty the iommu >>>>>>> backend is released and iommu_data is NULL. A container reference >>>>>>> doesn't give you what you're looking for. It implies nothing about the >>>>>>> iommu backend. >>>>>> >>>>>> >>>>>> Well. Backend is a part of a container and since a backend owns tables, a >>>>>> container owns them too. >>>>> >>>>> The IOMMU backend is accessed through the container, but that backend >>>>> is privileged by the groups it contains. Once those groups are gone, >>>>> the IOMMU backend is released, regardless of whatever reference you >>>>> have to the container itself such as you're attempting to do here. In >>>>> that sense, the container does not own those tables. >>>> >>>> So, the thing is that what KVM fundamentally needs is a handle on the >>>> container. KVM is essentially modelling the DMA address space of a >>>> single guest bus, and the container is what's attached to that. >>>> >>>> The first part of the problem is that KVM wants to basically invoke >>>> vfio_dma_map() operations without bouncing via qemu. Because >>>> vfio_dma_map() works on the container level, that's the handle that >>>> KVM needs to hold. >>>> >>>> The second part of the problem is that in order to reduce overhead >>>> further, we want to operate in real mode, which means bypassing most >>>> of the usual VFIO structure and going directly(ish) from the KVM >>>> hcall emulation to the IOMMU backend behind VFIO. This complicates >>>> matters a fair bit. Because it is, explicitly, a performance hack, >>>> some degree of ugliness is probably inevitable. >>>> >>>> Alexey - actually implementing this in two stages might make this >>>> clearer. The first stage wouldn't allow real mode, and would call >>>> through the same vfio_dma_map() path as qemu calls through now. The >>>> second stage would then put in place the necessary hacks to add real >>>> mode support. >>>> >>>>>> The problem I am trying to solve here is when KVM may release the >>>>>> iommu_table objects. >>>>>> >>>>>> "Set" ioctl() to KVM-spapr-tce-table (or KVM itself, does not really >>>>>> matter) makes a link between KVM-spapr-tce-table and container and KVM >>>>>> can >>>>>> start using tables (with referencing them). >>>>>> >>>>>> First I tried adding an "unset" ioctl to KVM-spapr-tce-table, called it >>>>>> from region_del() and this works if QEMU removes a window. However if >>>>>> QEMU >>>>>> removes a vfio-pci device, region_del() is not called and KVM does not >>>>>> get >>>>>> notified that it can release the iommu_table's because the >>>>>> KVM-spapr-tce-table remains alive and does not get destroyed (as it is >>>>>> still used by emulated devices or other containers). >>>>>> >>>>>> So it was suggested that we could do such "unset" somehow later assuming, >>>>>> for example, on every "set" I could check if some of currently attached >>>>>> containers are no more used - and this is where being able to know if >>>>>> there >>>>>> is no backend helps - KVM remembers a container pointer and can check >>>>>> this >>>>>> via vfio_container_get_iommu_data_ext(). >>>>>> >>>>>> The other option would be changing vfio_container_get_ext() to take a >>>>>> callback+opaque which container would call when it destroys iommu_data. >>>>>> This looks more intrusive and not very intuitive how to make it right - >>>>>> container would have to keep track of all registered external users and >>>>>> vfio_container_put_ext() would have to pass the same callback+opaque to >>>>>> unregister the exact external user. >>>>> >>>>> I'm not in favor of anything resembling the code above or extensions >>>>> beyond it, the container is the wrong place to do this. >>>>> >>>>>> Or I could store container file* in KVM. Then iommu_data would never be >>>>>> released until KVM-spapr-tce-table is destroyed. >>>>> >>>>> See above, holding a file pointer to the container doesn't do squat. >>>>> The groups that are held by the container empower the IOMMU backend, >>>>> references to the container itself don't matter. Those references will >>>>> not maintain the IOMMU data. >>>>> >>>>>> Recreating KVM-spapr-tce-table on every vfio-pci hotunplug (closing its >>>>>> fd >>>>>> would "unset" container from KVM-spapr-tce-table) is not an option as >>>>>> there >>>>>> still may be devices using this KVM-spapr-tce-table. >>>>>> >>>>>> What obvious and nice solution am I missing here? Thanks. >>>>> >>>>> The interactions with the IOMMU backend that seem relevant are >>>>> vfio_iommu_drivers_ops.{detach_group,release}. The kvm-vfio pseudo >>>>> device is also used to tell kvm about groups as they come and go and >>>>> has a way to check extensions, and thus properties of the IOMMU >>>>> backend. All of these are available for your {ab}use. Thanks, >>>> >>>> So, Alexey started trying to do this via the KVM-VFIO device, but it's >>>> a really bad fit. As noted above, fundamentally it's a container we >>>> need to attach to the kvm-spapr-tce-table object, since what that >>>> represents is a guest bus DMA address space, and by definition all the >>>> groups in a container must have the same DMA address space. >>> >>> That's all fine and good, but the point remains that a reference to the >>> container is no assurance of the iommu state. The iommu state is >>> maintained by the user and the groups attached to the container. If >>> the groups are removed, your container reference no long has any iommu >>> backing and iommu_data is worthless. The user can do this as well by >>> un-setting the iommu. I understand what you're trying to do, it's just >>> wrong. Thanks, >> >> I'm trying to figure out how to do this right, and it's not at all >> obvious. The container may be wrong, but that doesn't have the >> KVM-VFIO device any more useful. Attempting to do this at the group >> level is at least as wrong for the reasons I've mentioned elsewhere. >> > > I could create a new fd, one per iommu_table, the fd would reference the > iommu_table (not touching an iommu_table_group or a container), VFIO SPAPR > TCE backend would return it in VFIO_IOMMU_SPAPR_TCE_CREATE (ioctl which > creates windows) or I could add VFIO_IOMMU_SPAPR_TCE_GET_FD_BY_OFFSET; then > I'd pass this new fd to the KVM or KVM-spapr-tce-table to hook them up. To > release the reference, KVM-spapr-tce-table would have "unset" ioctl() > or/and on every "set" I would look if all attached tables have at least one > iommu_table_group attached, if none - release the table. > > This would make no change to generic VFIO code and very little change in > SPAPR TCE backend. Would that be acceptable or it is horrible again? Thanks.
Ping? -- Alexey
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