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Commit faeb7833 authored by Roman Kagan's avatar Roman Kagan Committed by Radim Krčmář
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kvm: x86: hyperv: guest->host event signaling via eventfd 



In Hyper-V, the fast guest->host notification mechanism is the
SIGNAL_EVENT hypercall, with a single parameter of the connection ID to
signal.

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: default avatarRoman Kagan <rkagan@virtuozzo.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
[asm/hyperv.h changes approved by KY Srinivasan. - Radim]
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
parent cbc0236a

Documentation/virtual/kvm/api.txt

+32 −0
Original line number Diff line number Diff line
@@ -3516,6 +3516,38 @@ Returns: 0 on success; -1 on error 
This ioctl can be used to unregister the guest memory region registered

with KVM_MEMORY_ENCRYPT_REG_REGION ioctl above.



4.113 KVM_HYPERV_EVENTFD



Capability: KVM_CAP_HYPERV_EVENTFD

Architectures: x86

Type: vm ioctl

Parameters: struct kvm_hyperv_eventfd (in)



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.  SIGNAL_EVENT hypercall with non-zero event flag number

(bits 24-31) still triggers a KVM_EXIT_HYPERV_HCALL user exit.



struct kvm_hyperv_eventfd {

	__u32 conn_id;

	__s32 fd;

	__u32 flags;

	__u32 padding[3];

};



The conn_id field should fit within 24 bits:



#define KVM_HYPERV_CONN_ID_MASK		0x00ffffff



The acceptable values for the flags field are:



#define KVM_HYPERV_EVENTFD_DEASSIGN	(1 << 0)



Returns: 0 on success,

	-EINVAL if conn_id or flags is outside the allowed range

	-ENOENT on deassign if the conn_id isn't registered

	-EEXIST on assign if the conn_id is already registered





5. The kvm_run structure

------------------------

arch/x86/include/asm/kvm_host.h

+2 −0
Original line number Diff line number Diff line
@@ -754,6 +754,8 @@ struct kvm_hv { 
	u64 hv_crash_ctl;



	HV_REFERENCE_TSC_PAGE tsc_ref;



	struct idr conn_to_evt;

};



enum kvm_irqchip_mode {

arch/x86/include/uapi/asm/hyperv.h

+2 −0
Original line number Diff line number Diff line
@@ -303,7 +303,9 @@ enum HV_GENERIC_SET_FORMAT { 
#define HV_STATUS_INVALID_HYPERCALL_CODE	2

#define HV_STATUS_INVALID_HYPERCALL_INPUT	3

#define HV_STATUS_INVALID_ALIGNMENT		4

#define HV_STATUS_INVALID_PARAMETER		5

#define HV_STATUS_INSUFFICIENT_MEMORY		11

#define HV_STATUS_INVALID_PORT_ID		17

#define HV_STATUS_INVALID_CONNECTION_ID		18

#define HV_STATUS_INSUFFICIENT_BUFFERS		19

arch/x86/kvm/hyperv.c

+102 −1
Original line number Diff line number Diff line
@@ -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 +1227,43 @@ static int kvm_hv_hypercall_complete_userspace(struct kvm_vcpu *vcpu) 
	return 1;

}



static u16 kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, bool fast, u64 param)

{

	struct eventfd_ctx *eventfd;



	if (unlikely(!fast)) {

		int ret;

		gpa_t gpa = param;



		if ((gpa & (__alignof__(param) - 1)) ||

		    offset_in_page(gpa) + sizeof(param) > PAGE_SIZE)

			return HV_STATUS_INVALID_ALIGNMENT;



		ret = kvm_vcpu_read_guest(vcpu, gpa, &param, sizeof(param));

		if (ret < 0)

			return HV_STATUS_INVALID_ALIGNMENT;

	}



	/*

	 * Per spec, bits 32-47 contain the extra "flag number".  However, we

	 * have no use for it, and in all known usecases it is zero, so just

	 * report lookup failure if it isn't.

	 */

	if (param & 0xffff00000000ULL)

		return HV_STATUS_INVALID_PORT_ID;

	/* remaining bits are reserved-zero */

	if (param & ~KVM_HYPERV_CONN_ID_MASK)

		return HV_STATUS_INVALID_HYPERCALL_INPUT;



	/* conn_to_evt is protected by vcpu->kvm->srcu */

	eventfd = idr_find(&vcpu->kvm->arch.hyperv.conn_to_evt, param);

	if (!eventfd)

		return HV_STATUS_INVALID_PORT_ID;



	eventfd_signal(eventfd, 1);

	return HV_STATUS_SUCCESS;

}



int kvm_hv_hypercall(struct kvm_vcpu *vcpu)

{

	u64 param, ingpa, outgpa, ret;
@@ -1276,8 +1314,12 @@ 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_PORT_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 +1347,67 @@ 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)

{

	struct eventfd_ctx *eventfd;

	int i;



	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, u32 conn_id, int fd)

{

	struct kvm_hv *hv = &kvm->arch.hyperv;

	struct eventfd_ctx *eventfd;

	int ret;



	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, u32 conn_id)

{

	struct kvm_hv *hv = &kvm->arch.hyperv;

	struct eventfd_ctx *eventfd;



	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 0;

}



int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args)

{

	if ((args->flags & ~KVM_HYPERV_EVENTFD_DEASSIGN) ||

	    (args->conn_id & ~KVM_HYPERV_CONN_ID_MASK))

		return -EINVAL;



	if (args->flags == KVM_HYPERV_EVENTFD_DEASSIGN)

		return kvm_hv_eventfd_deassign(kvm, args->conn_id);

	return kvm_hv_eventfd_assign(kvm, args->conn_id, args->fd);

}

arch/x86/kvm/hyperv.h

+1 −0
Original line number Diff line number Diff line
@@ -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