On Fri, 9 Dec 2016 18:53:43 +1100
Alexey Kardashevskiy <aik@xxxxxxxxx> wrote:
> On 09/12/16 04:55, Alex Williamson wrote:
> > On Thu, 8 Dec 2016 19:19:56 +1100
> > Alexey Kardashevskiy <aik@xxxxxxxxx> wrote:
> >
> >> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
> >> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
> >> without passing them to user space which saves time on switching
> >> to user space and back.
> >>
> >> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
> >> KVM tries to handle a TCE request in the real mode, if failed
> >> it passes the request to the virtual mode to complete the operation.
> >> If it a virtual mode handler fails, the request is passed to
> >> the user space; this is not expected to happen though.
> >>
> >> To avoid dealing with page use counters (which is tricky in real mode),
> >> this only accelerates SPAPR TCE IOMMU v2 clients which are required
> >> to pre-register the userspace memory. The very first TCE request will
> >> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
> >> of the TCE table (iommu_table::it_userspace) is not allocated till
> >> the very first mapping happens and we cannot call vmalloc in real mode.
> >>
> >> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
> >> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
> >> and associates a physical IOMMU table with the SPAPR TCE table (which
> >> is a guest view of the hardware IOMMU table). The iommu_table object
> >> is referenced so we do not have to retrieve in real mode when hypercall
> >> happens.
> >>
> >> This does not implement the UNSET counterpart as there is no use for it -
> >> once the acceleration is enabled, the existing userspace won't
> >> disable it unless a VFIO container is detroyed so this adds necessary
> >> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
> >>
> >> This uses the kvm->lock mutex to protect against a race between
> >> the VFIO KVM device's kvm_vfio_destroy() and SPAPR TCE table fd's
> >> release() callback.
> >>
> >> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
> >> space.
> >>
> >> This finally makes use of vfio_external_user_iommu_id() which was
> >> introduced quite some time ago and was considered for removal.
> >>
> >> Tests show that this patch increases transmission speed from 220MB/s
> >> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> >> ---
> >> Documentation/virtual/kvm/devices/vfio.txt | 21 +-
> >> arch/powerpc/include/asm/kvm_host.h | 8 +
> >> arch/powerpc/include/asm/kvm_ppc.h | 5 +
> >> include/uapi/linux/kvm.h | 8 +
> >> arch/powerpc/kvm/book3s_64_vio.c | 302 +++++++++++++++++++++++++++++
> >> arch/powerpc/kvm/book3s_64_vio_hv.c | 178 +++++++++++++++++
> >> arch/powerpc/kvm/powerpc.c | 2 +
> >> virt/kvm/vfio.c | 108 +++++++++++
> >> 8 files changed, 630 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
> >> index ef51740c67ca..ddb5a6512ab3 100644
> >> --- a/Documentation/virtual/kvm/devices/vfio.txt
> >> +++ b/Documentation/virtual/kvm/devices/vfio.txt
> >> @@ -16,7 +16,24 @@ 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: attaches a guest visible TCE table
> >> + allocated by sPAPR KVM.
> >> + kvm_device_attr.addr points to a struct:
> >>
> >> -For each, kvm_device_attr.addr points to an int32_t file descriptor
> >> -for the VFIO group.
> >> + struct kvm_vfio_spapr_tce {
> >> + __u32 argsz;
> >> + __s32 groupfd;
> >> + __s32 tablefd;
> >> + __u8 pad[4];
> >> + };
> >> +
> >> + where
> >> + @argsz is the size of kvm_vfio_spapr_tce_liobn;
> >> + @groupfd is a file descriptor for a VFIO group;
> >> + @tablefd is a file descriptor for a TCE table allocated via
> >> + KVM_CREATE_SPAPR_TCE.
> >> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> >> index 28350a294b1e..94774503c70d 100644
> >> --- a/arch/powerpc/include/asm/kvm_host.h
> >> +++ b/arch/powerpc/include/asm/kvm_host.h
> >> @@ -191,6 +191,13 @@ struct kvmppc_pginfo {
> >> atomic_t refcnt;
> >> };
> >>
> >> +struct kvmppc_spapr_tce_iommu_table {
> >> + struct rcu_head rcu;
> >> + struct list_head next;
> >> + struct iommu_table *tbl;
> >> + atomic_t refs;
> >> +};
> >> +
> >> struct kvmppc_spapr_tce_table {
> >> struct list_head list;
> >> struct kvm *kvm;
> >> @@ -199,6 +206,7 @@ struct kvmppc_spapr_tce_table {
> >> u32 page_shift;
> >> u64 offset; /* in pages */
> >> u64 size; /* window size in pages */
> >> + struct list_head iommu_tables;
> >> struct page *pages[0];
> >> };
> >>
> >> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> >> index 0a21c8503974..17b947a0060d 100644
> >> --- a/arch/powerpc/include/asm/kvm_ppc.h
> >> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> >> @@ -163,6 +163,11 @@ extern long kvmppc_prepare_vrma(struct kvm *kvm,
> >> extern void kvmppc_map_vrma(struct kvm_vcpu *vcpu,
> >> struct kvm_memory_slot *memslot, unsigned long porder);
> >> extern int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu);
> >> +extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm,
> >> + int tablefd,
> >> + struct iommu_group *grp);
> >> +extern void kvm_spapr_tce_detach_iommu_group(struct kvm *kvm,
> >> + struct iommu_group *grp);
> >>
> >> extern long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> >> struct kvm_create_spapr_tce_64 *args);
> >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> >> index 810f74317987..9e4025724e28 100644
> >> --- a/include/uapi/linux/kvm.h
> >> +++ b/include/uapi/linux/kvm.h
> >> @@ -1068,6 +1068,7 @@ 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 3
> >>
> >> enum kvm_device_type {
> >> KVM_DEV_TYPE_FSL_MPIC_20 = 1,
> >> @@ -1089,6 +1090,13 @@ enum kvm_device_type {
> >> KVM_DEV_TYPE_MAX,
> >> };
> >>
> >> +struct kvm_vfio_spapr_tce {
> >> + __u32 argsz;
> >> + __s32 groupfd;
> >> + __s32 tablefd;
> >> + __u8 pad[4];
> >> +};
> >
> > I assume you're implementing argsz and padding for future expansion,
> > but it doesn't really work. Presumably argsz would be set to 16, so
> > the only way that the kernel will ever know something has changed would
> > be to make it bigger, so the padding bytes are really reserved, and
> > then it's not clear why we have padding at all. If you replaced the
> > padding with a __u32 flags, then we could actually have some room to
> > architect expansion, but as it is we might as well drop both argsz and
> > padding.
>
> Ah, right, sorry, did not pay attention to this bit this time. I'll replace
> pad with flags and move to argsz.
>
>
> >
> >> +
> >> /*
> >> * ioctls for VM fds
> >> */
> > ...
> >> --- a/virt/kvm/vfio.c
> >> +++ b/virt/kvm/vfio.c
> >> @@ -20,6 +20,10 @@
> >> #include <linux/vfio.h>
> >> #include "vfio.h"
> >>
> >> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> >> +#include <asm/kvm_ppc.h>
> >> +#endif
> >> +
> >> struct kvm_vfio_group {
> >> struct list_head node;
> >> struct vfio_group *vfio_group;
> >> @@ -76,6 +80,22 @@ static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
> >> return ret > 0;
> >> }
> >>
> >> +static int kvm_vfio_external_user_iommu_id(struct vfio_group *vfio_group)
> >> +{
> >> + int (*fn)(struct vfio_group *);
> >> + int ret = -1;
> >> +
> >> + fn = symbol_get(vfio_external_user_iommu_id);
> >> + if (!fn)
> >> + return ret;
> >> +
> >> + ret = fn(vfio_group);
> >> +
> >> + symbol_put(vfio_external_user_iommu_id);
> >> +
> >> + return ret;
> >> +}
> >> +
> >> /*
> >> * 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
> >> @@ -110,6 +130,22 @@ static void kvm_vfio_update_coherency(struct kvm_device *dev)
> >> mutex_unlock(&kv->lock);
> >> }
> >>
> >> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> >> +static void kvm_vfio_spapr_detach_iommu_group(struct kvm *kvm,
> >> + struct vfio_group *vfio_group)
> >> +{
> >> + int group_id;
> >> + struct iommu_group *grp;
> >> +
> >> + group_id = kvm_vfio_external_user_iommu_id(vfio_group);
> >> + grp = iommu_group_get_by_id(group_id);
> >> + if (grp) {
> >> + kvm_spapr_tce_detach_iommu_group(kvm, grp);
> >> + iommu_group_put(grp);
> >> + }
> >> +}
> >> +#endif
> >
> >
> > I wonder if you could use the new vfio group notifier to avoid tainting
> > this code with SPAPR_TCE #ifdefs. Thanks,
>
> I cannot see how... The new notifier sets kvm to a group, I need the
> opposite - attach a group to kvm and not just to KVM but to a specific KVM
> SPAPR TCE fd (which is a child object of KVM and which owns a LIOBN bus id).
>
> The only way I see how I can avoid tainting this code is adding another
> ioctl() to PPC KVM (or its child object - SPAPR TCE object), and I tried
> that few years ago and I was told to add a KVM device or even reuse VFIO
> KVM device.
>
> What am I missing here?
You would still need a KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE, but the ugly
part of encompassing this all in #ifdefs is that we call
kvm_spapr_tce_{at,de}tach_iommu_group() directly. The notifier would
sort of make it like an arch callback, vfio core would set these
attributes and broadcast them to notifier callbacks, on non-spapr-tce
platforms nobody would be listening for those notifications.
Ultimately I don't know how much cleaner it makes things, but it maybe
avoids spapr-tce #ifdefs leaking into every layer of the stack. Thanks,
Alex
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