Re: [PATCH v3] KVM: PPC: vfio kvm device: support spapr tce

From: Alex Williamson
Date: Thu Nov 21 2013 - 15:30:41 EST

On Thu, 2013-11-21 at 12:22 +1100, Alexey Kardashevskiy wrote:
> On 11/21/2013 07:57 AM, Alex Williamson wrote:
> > On Wed, 2013-11-20 at 16:18 +1100, Alexey Kardashevskiy wrote:
> >> In addition to the external VFIO user API, a VFIO KVM device
> >> has been introduced recently.
> >>
> >> sPAPR TCE IOMMU is para-virtualized and the guest does map/unmap
> >> via hypercalls which take a logical bus id (LIOBN) as a target IOMMU
> >> identifier. LIOBNs are made up and linked to IOMMU groups by the user
> >> space. In order to accelerate IOMMU operations in the KVM, we need
> >> to tell KVM the information about LIOBN-to-group mapping.
> >>
> >> For that, a new KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN parameter
> >> is added. It accepts a pair of a VFIO group fd and LIOBN.
> >>
> >> This also adds a new kvm_vfio_find_group_by_liobn() function which
> >> receives kvm struct, LIOBN and a callback. As it increases the IOMMU
> >> group use counter, the KVMr is required to pass a callback which
> >> called when the VFIO group is about to be removed VFIO-KVM tracking so
> >> the KVM is able to call iommu_group_put() to release the IOMMU group.
> >>
> >> The KVM uses kvm_vfio_find_group_by_liobn() once per KVM run and caches
> >> the result in kvm_arch. iommu_group_put() for all groups will be called
> >> when KVM finishes (in the SPAPR TCE in KVM enablement patch).
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> >> ---
> >> Changes:
> >> v3:
> >> * total rework
> >> * added a release callback into kvm_vfio_find_group_by_liobn so now
> >> the user of the API can get a notification if the group is about to
> >> disappear
> >> ---
> >> Documentation/virtual/kvm/devices/vfio.txt | 19 ++++-
> >> arch/powerpc/kvm/Kconfig | 1 +
> >> arch/powerpc/kvm/Makefile | 3 +
> >> include/linux/kvm_host.h | 18 +++++
> >> include/uapi/linux/kvm.h | 7 ++
> >> virt/kvm/vfio.c | 116 ++++++++++++++++++++++++++++-
> >> 6 files changed, 161 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
> >> index ef51740..7ecb3b2 100644
> >> --- a/Documentation/virtual/kvm/devices/vfio.txt
> >> +++ b/Documentation/virtual/kvm/devices/vfio.txt
> >> @@ -16,7 +16,22 @@ Groups:
> >>
> >> KVM_DEV_VFIO_GROUP attributes:
> >> KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
> >> + kvm_device_attr.addr points to an int32_t file descriptor
> >> + for the VFIO group.
> >> +
> >> KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking
> >> + kvm_device_attr.addr points to an int32_t file descriptor
> >> + for the VFIO group.
> >> +
> >> + KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: sets a liobn for a VFIO group
> >> + kvm_device_attr.addr points to a struct:
> >> + struct kvm_vfio_spapr_tce_liobn {
> >> + __u32 argsz;
> >> + __u32 fd;
> >
> > fds are signed, __s32
> >
> >> + __u32 liobn;
> >> + };
> >> + where
> >> + @argsz is a struct size;
> >> + @fd is a file descriptor for a VFIO group;
> >> + @liobn is a logical bus id to be associated with the group.
> >>
> >> -For each, kvm_device_attr.addr points to an int32_t file descriptor
> >> -for the VFIO group.
> >> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
> >> index 61b3535..d1b7f64 100644
> >> --- a/arch/powerpc/kvm/Kconfig
> >> +++ b/arch/powerpc/kvm/Kconfig
> >> @@ -60,6 +60,7 @@ config KVM_BOOK3S_64
> >> select KVM_BOOK3S_64_HANDLER
> >> select KVM
> >> select SPAPR_TCE_IOMMU
> >> + select KVM_VFIO
> >> ---help---
> >> Support running unmodified book3s_64 and book3s_32 guest kernels
> >> in virtual machines on book3s_64 host processors.
> >> diff --git a/arch/powerpc/kvm/Makefile b/arch/powerpc/kvm/Makefile
> >> index 6646c95..2438d2e 100644
> >> --- a/arch/powerpc/kvm/Makefile
> >> +++ b/arch/powerpc/kvm/Makefile
> >> @@ -87,6 +87,9 @@ kvm-book3s_64-builtin-objs-$(CONFIG_KVM_BOOK3S_64_HV) := \
> >> kvm-book3s_64-objs-$(CONFIG_KVM_XICS) += \
> >> book3s_xics.o
> >>
> >> +kvm-book3s_64-objs-$(CONFIG_KVM_VFIO) += \
> >> + $(KVM)/vfio.o \
> >> +
> >> kvm-book3s_64-module-objs := \
> >> $(KVM)/kvm_main.o \
> >> $(KVM)/eventfd.o \
> >> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> >> index 88ff96a..1d2ad5e 100644
> >> --- a/include/linux/kvm_host.h
> >> +++ b/include/linux/kvm_host.h
> >> @@ -1112,5 +1112,23 @@ static inline bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu)
> >> }
> >>
> >> #endif /* CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT */
> >> +
> >> +typedef void (*kvm_vfio_release_group_callback)(struct kvm *kvm,
> >> + unsigned long liobn);
> >
> > liobn was said to be __u32 in kvm_vfio_spapr_tce_liobn above, here it's
> > unsigned long?
>
>
> PAPR spec says it is 32 bit and kvm_vfio_spapr_tce_liobn is a binary
> interface (ABI?) so I want it to be precise.
>
> However kvmppc_get_gpr() (used to parse hypercall parameters such as liobn)
> return unsigned long. So inside the kernel I use unsigned long.
>
> So what does make sense to change here?

Perhaps nothing if that's clear to those familiar with PAPR. Thanks,

Alex


> >
> >> +
> >> +#if defined(CONFIG_KVM_VFIO) && defined(CONFIG_SPAPR_TCE_IOMMU)
> >> +
> >> +extern struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
> >> + unsigned long liobn, kvm_vfio_release_group_callback cb);
> >> +
> >> +#else
> >> +
> >> +static inline struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
> >> + unsigned long liobn, ikvm_vfio_release_group_callback cb)
> >> +{
> >> + return NULL;
> >> +}
> >> +#endif /* CONFIG_KVM_VFIO && CONFIG_SPAPR_TCE_IOMMU */
> >> +
> >> #endif
> >>
> >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> >> index 7c1a349..3d77dde 100644
> >> --- a/include/uapi/linux/kvm.h
> >> +++ b/include/uapi/linux/kvm.h
> >> @@ -847,6 +847,13 @@ struct kvm_device_attr {
> >> #define KVM_DEV_VFIO_GROUP 1
> >> #define KVM_DEV_VFIO_GROUP_ADD 1
> >> #define KVM_DEV_VFIO_GROUP_DEL 2
> >> +#define KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN 3
> >> +
> >> +struct kvm_vfio_spapr_tce_liobn {
> >> + __u32 argsz;
> >> + __u32 fd;
> >> + __u32 liobn;
> >> +};
> >>
> >> /*
> >> * ioctls for VM fds
> >> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> >> index ca4260e..448910d 100644
> >> --- a/virt/kvm/vfio.c
> >> +++ b/virt/kvm/vfio.c
> >> @@ -22,6 +22,12 @@
> >> struct kvm_vfio_group {
> >> struct list_head node;
> >> struct vfio_group *vfio_group;
> >> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> >> + struct {
> >> + unsigned long liobn;
> >> + kvm_vfio_release_group_callback cb;
> >> + } spapr_tce;
> >> +#endif
> >> };
> >>
> >> struct kvm_vfio {
> >> @@ -59,6 +65,51 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
> >> symbol_put(vfio_group_put_external_user);
> >> }
> >>
> >> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> >> +struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
> >> + unsigned long liobn, kvm_vfio_release_group_callback cb)
> >> +{
> >> + struct kvm_vfio_group *kvg;
> >> + int group_id;
> >> + struct iommu_group *grp;
> >> + struct kvm_vfio *kv = NULL;
> >> + struct kvm_device *tmp;
> >> +
> >> + if (!cb)
> >> + return NULL;
> >
> > Is it worthwhile to use ERR_PTR(-EINVAL) here and the caller can use
> > IS_ERR()?
> >
> >> +
> >> + /* Find a VFIO KVM device */
> >> + list_for_each_entry(tmp, &kvm->devices, vm_node) {
> >> + if (tmp->ops != &kvm_vfio_ops)
> >> + continue;
> >> +
> >> + kv = tmp->private;
> >> + break;
> >> + }
> >> +
> >> + if (!kv)
> >> + return NULL;
> >
> > ERR_PTR(-EFAULT)? EIO?
> >
> >> +
> >> + /* Find a group */
> >
> > Still ignoring kv->lock
> >
> >> + list_for_each_entry(kvg, &kv->group_list, node) {
> >> + if (kvg->spapr_tce.liobn != liobn)
> >> + continue;
> >> +
> >> + if (kvg->spapr_tce.cb)
> >> + return NULL;
> >
> > ERR_PTR(-EBUSY)?
> >
> >> +
> >> + kvg->spapr_tce.cb = cb;
> >> + group_id = vfio_external_user_iommu_id(kvg->vfio_group);
> >> + grp = iommu_group_get_by_id(group_id);
> >> +
> >> + return grp;
> >> + }
> >> +
> >> + return NULL;
> >
> > ERR_PTR(-ENODEV)?
> >
> >> +}
> >> +EXPORT_SYMBOL_GPL(kvm_vfio_find_group_by_liobn);
> >> +#endif
> >> +
> >> /*
> >> * Groups can use the same or different IOMMU domains. If the same then
> >> * adding a new group may change the coherency of groups we've previously
> >> @@ -170,6 +221,11 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
> >> continue;
> >>
> >> list_del(&kvg->node);
> >> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> >> + if (kvg->spapr_tce.cb)
> >> + kvg->spapr_tce.cb(dev->kvm,
> >> + kvg->spapr_tce.liobn);
> >> +#endif
> >> kvm_vfio_group_put_external_user(kvg->vfio_group);
> >> kfree(kvg);
> >> ret = 0;
> >> @@ -183,6 +239,62 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
> >> kvm_vfio_update_coherency(dev);
> >>
> >> return ret;
> >> +
> >> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> >> + case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: {
> >> + struct kvm_vfio_spapr_tce_liobn param;
> >> + unsigned long minsz;
> >> + struct kvm_vfio *kv = dev->private;
> >> + struct vfio_group *vfio_group;
> >> + struct kvm_vfio_group *kvg;
> >> + struct fd f;
> >> +
> >> + minsz = offsetofend(struct kvm_vfio_spapr_tce_liobn, liobn);
> >> +
> >> + if (copy_from_user(&param, (void __user *)arg, minsz))
> >> + return -EFAULT;
> >> +
> >> + if (param.argsz < minsz)
> >> + return -EINVAL;
> >> +
> >> + if (copy_from_user(&param, (void __user *)arg, minsz))
> >> + return -EFAULT;
> >
> > copy_from_user twice? Extra copy here?
>
>
> Oh. All I wanted was to read minsz first but I cut-n-pasted too blindely :)
>
> >
> >> +
> >> + f = fdget(param.fd);
> >> + if (!f.file)
> >> + return -EBADF;
> >> +
> >> + vfio_group = kvm_vfio_group_get_external_user(f.file);
> >> + fdput(f);
> >> +
> >> + if (IS_ERR(vfio_group))
> >> + return PTR_ERR(vfio_group);
> >> +
> >> + ret = -ENOENT;
> >> +
> >> + mutex_lock(&kv->lock);
> >> +
> >> + list_for_each_entry(kvg, &kv->group_list, node) {
> >> + if (kvg->vfio_group != vfio_group)
> >> + continue;
> >> +
> >> + if (kvg->spapr_tce.liobn) {
> >> + ret = -EBUSY;
> >> + break;
> >> + }
> >
> > Is zero not an liobn that can be used by userspace?
>
> Good point, thanks. I thought zero cannot be used but by spec -1 is reserved
>
>
> > Is it intentional
> > that there's no way to unset or change the group/liobn mapping? Thanks,
>
>
> I do not see why we would want to disable once enabled acceleration. Group
> removal should clear it though so we are good.
>
> Thanks for the review and patience :)
>
>
> >
> > Alex
> >
> >> +
> >> + kvg->spapr_tce.liobn = param.liobn;
> >> + ret = 0;
> >> + break;
> >> + }
> >> +
> >> + mutex_unlock(&kv->lock);
> >> +
> >> + kvm_vfio_group_put_external_user(vfio_group);
> >> +
> >> + return ret;
> >> + }
> >> +#endif /* CONFIG_SPAPR_TCE_IOMMU */
> >> }
> >>
> >> return -ENXIO;
> >> @@ -207,9 +319,11 @@ static int kvm_vfio_has_attr(struct kvm_device *dev,
> >> switch (attr->attr) {
> >> case KVM_DEV_VFIO_GROUP_ADD:
> >> case KVM_DEV_VFIO_GROUP_DEL:
> >> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> >> + case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN:
> >> +#endif
> >> return 0;
> >> }
> >> -
> >> break;
> >> }
> >>
> >
> >
> >
>
>



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