Roman Kagan <rkagan@xxxxxxxxxxxxx> writes:
> In Hyper-V, the fast guest->host notification mechanism is the
> SIGNAL_EVENT hypercall, with a single parameter of the connection ID to
> signal.
(I may be missing something important...)
I'm not sure how Windows does that but Linux Hyper-V drivers use
hard-coded VMBUS_EVENT_CONNECTION_ID (2) for all HVCALL_SIGNAL_EVENT
hypercalls. According to the spec, this id comes from HvConnectPort
hypercall which is executed by the root partition -- not sure how it's
supposed to be passed down to the guest.
So in case the situation in Windows is not any different the connection
ID parameter will always be 2 so we may as well just omit it) Or,
alternatively, we can probably add both VMBUS_MESSAGE_CONNECTION_ID and
VMBUS_MONITOR_CONNECTION_ID to the mechanism...
>
> Currently this hypercall incurs a user exit and requires the userspace
> to decode the parameters and trigger the notification of the potentially
> different I/O context.
>
> To avoid the costly user exit, process this hypercall and signal the
> corresponding eventfd in KVM, similar to ioeventfd. The association
> between the connection id and the eventfd is established via the newly
> introduced KVM_HYPERV_EVENTFD ioctl, and maintained in an
> (srcu-protected) IDR.
>
> Signed-off-by: Roman Kagan <rkagan@xxxxxxxxxxxxx>
> ---
> Documentation/virtual/kvm/api.txt | 23 ++++++++
> arch/x86/include/asm/kvm_host.h | 2 +
> arch/x86/kvm/hyperv.h | 1 +
> include/uapi/linux/kvm.h | 13 +++++
> arch/x86/kvm/hyperv.c | 115 +++++++++++++++++++++++++++++++++++++-
> arch/x86/kvm/x86.c | 10 ++++
> 6 files changed, 163 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index f670e4b9e7f3..e4f319add8b7 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3394,6 +3394,29 @@ invalid, if invalid pages are written to (e.g. after the end of memory)
> or if no page table is present for the addresses (e.g. when using
> hugepages).
>
> +4.109 KVM_HYPERV_EVENTFD
> +
> +Capability: KVM_CAP_HYPERV_EVENTFD
> +Architectures: x86
> +Type: vm ioctl
> +Parameters: struct kvm_hyperv_eventfd (in)
> +Returns: 0 on success, !0 on error
> +
> +This ioctl (un)registers an eventfd to receive notifications from the guest on
> +the specified Hyper-V connection id through the SIGNAL_EVENT hypercall, without
> +causing a user exit.
> +
> +struct kvm_hyperv_eventfd {
> + __u32 conn_id;
> + __s32 fd;
> + __u32 flags;
> + __u32 padding[3];
> +};
> +
> +The acceptable values for the flags field:
> +
> +#define KVM_HYPERV_EVENTFD_DEASSIGN (1 << 0)
> +
> 5. The kvm_run structure
> ------------------------
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 1bfb99770c34..0d37eb837991 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -739,6 +739,8 @@ struct kvm_hv {
> u64 hv_crash_ctl;
>
> HV_REFERENCE_TSC_PAGE tsc_ref;
> +
> + struct idr conn_to_evt;
> };
>
> enum kvm_irqchip_mode {
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index cc2468244ca2..837465d69c6d 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -90,5 +90,6 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm,
>
> void kvm_hv_init_vm(struct kvm *kvm);
> void kvm_hv_destroy_vm(struct kvm *kvm);
> +int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args);
>
> #endif
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 282d7613fce8..465f45c13cdc 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -932,6 +932,7 @@ struct kvm_ppc_resize_hpt {
> #define KVM_CAP_HYPERV_SYNIC2 148
> #define KVM_CAP_HYPERV_VP_INDEX 149
> #define KVM_CAP_S390_AIS_MIGRATION 150
> +#define KVM_CAP_HYPERV_EVENTFD 151
>
> #ifdef KVM_CAP_IRQ_ROUTING
>
> @@ -1359,6 +1360,8 @@ struct kvm_s390_ucas_mapping {
> #define KVM_S390_GET_CMMA_BITS _IOWR(KVMIO, 0xb8, struct kvm_s390_cmma_log)
> #define KVM_S390_SET_CMMA_BITS _IOW(KVMIO, 0xb9, struct kvm_s390_cmma_log)
>
> +#define KVM_HYPERV_EVENTFD _IOW(KVMIO, 0xba, struct kvm_hyperv_eventfd)
> +
> #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
> #define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
> #define KVM_DEV_ASSIGN_MASK_INTX (1 << 2)
> @@ -1419,4 +1422,14 @@ struct kvm_assigned_msix_entry {
> #define KVM_ARM_DEV_EL1_PTIMER (1 << 1)
> #define KVM_ARM_DEV_PMU (1 << 2)
>
> +struct kvm_hyperv_eventfd {
> + __u32 conn_id;
> + __s32 fd;
> + __u32 flags;
> + __u32 padding[3];
> +};
> +
> +#define KVM_HYPERV_CONN_ID_BITS 24
> +#define KVM_HYPERV_EVENTFD_DEASSIGN (1 << 0)
> +
> #endif /* __LINUX_KVM_H */
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 015fb06c7522..d2e8915546b1 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -29,6 +29,7 @@
> #include <linux/kvm_host.h>
> #include <linux/highmem.h>
> #include <linux/sched/cputime.h>
> +#include <linux/eventfd.h>
>
> #include <asm/apicdef.h>
> #include <trace/events/kvm.h>
> @@ -1226,6 +1227,54 @@ static int kvm_hv_hypercall_complete_userspace(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> +static u16 hvcall_sigevent_param(struct kvm_vcpu *vcpu, gpa_t gpa, u32 *conn_id)
> +{
> + struct page *page;
> + void *pg;
> + struct hv_input_signal_event *msg;
> +
> + if ((gpa & (__alignof__(*msg) - 1)) ||
> + offset_in_page(gpa) + sizeof(*msg) > PAGE_SIZE)
> + return HV_STATUS_INVALID_ALIGNMENT;
> +
> + page = kvm_vcpu_gfn_to_page(vcpu, gpa >> PAGE_SHIFT);
> + if (is_error_page(page))
> + return HV_STATUS_INSUFFICIENT_MEMORY;
> +
> + pg = kmap_atomic(page);
> + msg = pg + offset_in_page(gpa);
> + *conn_id = msg->connectionid.u.id + msg->flag_number;
> + kunmap_atomic(pg);
> + return HV_STATUS_SUCCESS;
> +}
> +
> +static u16 kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, bool fast, u64 ingpa)
> +{
> + u16 ret;
> + u32 conn_id;
> + int idx;
> + struct eventfd_ctx *eventfd;
> +
> + if (likely(fast))
> + conn_id = (ingpa & 0xffffffff) + ((ingpa >> 32) & 0xffff);
> + else {
> + ret = hvcall_sigevent_param(vcpu, ingpa, &conn_id);
> + if (ret != HV_STATUS_SUCCESS)
> + return ret;
> + }
> +
> + if (conn_id & ~((1 << KVM_HYPERV_CONN_ID_BITS) - 1))
> + return HV_STATUS_INVALID_CONNECTION_ID;
> +
> + idx = srcu_read_lock(&vcpu->kvm->srcu);
> + eventfd = idr_find(&vcpu->kvm->arch.hyperv.conn_to_evt, conn_id);
> + if (eventfd)
> + eventfd_signal(eventfd, 1);
> + srcu_read_unlock(&vcpu->kvm->srcu, idx);
> +
> + return eventfd ? HV_STATUS_SUCCESS : HV_STATUS_INVALID_CONNECTION_ID;
> +}
> +
> int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> {
> u64 param, ingpa, outgpa, ret;
> @@ -1276,8 +1325,12 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> case HVCALL_NOTIFY_LONG_SPIN_WAIT:
> kvm_vcpu_on_spin(vcpu, true);
> break;
> - case HVCALL_POST_MESSAGE:
> case HVCALL_SIGNAL_EVENT:
> + res = kvm_hvcall_signal_event(vcpu, fast, ingpa);
> + if (res != HV_STATUS_INVALID_CONNECTION_ID)
> + break;
> + /* maybe userspace knows this conn_id: fall through */
> + case HVCALL_POST_MESSAGE:
> /* don't bother userspace if it has no way to handle it */
> if (!vcpu_to_synic(vcpu)->active) {
> res = HV_STATUS_INVALID_HYPERCALL_CODE;
> @@ -1305,8 +1358,68 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> void kvm_hv_init_vm(struct kvm *kvm)
> {
> mutex_init(&kvm->arch.hyperv.hv_lock);
> + idr_init(&kvm->arch.hyperv.conn_to_evt);
> }
>
> void kvm_hv_destroy_vm(struct kvm *kvm)
> {
> + int i;
> + struct eventfd_ctx *eventfd;
> +
> + idr_for_each_entry(&kvm->arch.hyperv.conn_to_evt, eventfd, i)
> + eventfd_ctx_put(eventfd);
> + idr_destroy(&kvm->arch.hyperv.conn_to_evt);
> +}
> +
> +static int kvm_hv_eventfd_assign(struct kvm *kvm, int conn_id, int fd)
> +{
> + int ret;
> + struct eventfd_ctx *eventfd;
> + struct kvm_hv *hv = &kvm->arch.hyperv;
> +
> + eventfd = eventfd_ctx_fdget(fd);
> + if (IS_ERR(eventfd))
> + return PTR_ERR(eventfd);
> +
> + mutex_lock(&hv->hv_lock);
> + ret = idr_alloc(&hv->conn_to_evt, eventfd, conn_id, conn_id + 1,
> + GFP_KERNEL);
> + mutex_unlock(&hv->hv_lock);
> +
> + if (ret >= 0)
> + return 0;
> +
> + if (ret == -ENOSPC)
> + ret = -EEXIST;
> + eventfd_ctx_put(eventfd);
> + return ret;
> +}
> +
> +static int kvm_hv_eventfd_deassign(struct kvm *kvm, int conn_id)
> +{
> + int ret;
> + struct eventfd_ctx *eventfd;
> + struct kvm_hv *hv = &kvm->arch.hyperv;
> +
> + mutex_lock(&hv->hv_lock);
> + eventfd = idr_remove(&hv->conn_to_evt, conn_id);
> + mutex_unlock(&hv->hv_lock);
> +
> + if (!eventfd)
> + return -ENOENT;
> +
> + synchronize_srcu(&kvm->srcu);
> + eventfd_ctx_put(eventfd);
> + return ret;
> +}
> +
> +int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args)
> +{
> + if ((args->flags & ~KVM_HYPERV_EVENTFD_DEASSIGN) ||
> + (args->conn_id & ~((1 << KVM_HYPERV_CONN_ID_BITS) - 1)))
> + return -EINVAL;
> +
> + return args->flags == KVM_HYPERV_EVENTFD_DEASSIGN ?
> + kvm_hv_eventfd_deassign(kvm, args->conn_id) :
> + kvm_hv_eventfd_assign(kvm, args->conn_id, args->fd);
> }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0fe479d4b82c..2c786682f6f6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2686,6 +2686,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_HYPERV_SYNIC:
> case KVM_CAP_HYPERV_SYNIC2:
> case KVM_CAP_HYPERV_VP_INDEX:
> + case KVM_CAP_HYPERV_EVENTFD:
> case KVM_CAP_PCI_SEGMENT:
> case KVM_CAP_DEBUGREGS:
> case KVM_CAP_X86_ROBUST_SINGLESTEP:
> @@ -4281,6 +4282,15 @@ long kvm_arch_vm_ioctl(struct file *filp,
> r = kvm_vm_ioctl_enable_cap(kvm, &cap);
> break;
> }
> + case KVM_HYPERV_EVENTFD: {
> + struct kvm_hyperv_eventfd hvevfd;
> +
> + r = -EFAULT;
> + if (copy_from_user(&hvevfd, argp, sizeof(hvevfd)))
> + goto out;
> + r = kvm_vm_ioctl_hv_eventfd(kvm, &hvevfd);
> + break;
> + }
> default:
> r = -ENOTTY;
> }
--
Vitaly
