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From:   Elliot Berman <quic_eberman@quicinc.com>
To:     Alex Elder <elder@linaro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Elliot Berman <quic_eberman@quicinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>
CC:     Murali Nalajala <quic_mnalajal@quicinc.com>,
        Trilok Soni <quic_tsoni@quicinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@quicinc.com>,
        Carl van Schaik <quic_cvanscha@quicinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Bjorn Andersson <andersson@kernel.org>,
        "Konrad Dybcio" <konrad.dybcio@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        Andy Gross <agross@kernel.org>,
        Jassi Brar <jassisinghbrar@gmail.com>,
        <linux-arm-msm@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-doc@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
Subject: [PATCH v13 20/24] virt: gunyah: Add proxy-scheduled vCPUs
Date:   Tue, 9 May 2023 13:47:57 -0700
Message-ID: <20230509204801.2824351-21-quic_eberman@quicinc.com>
In-Reply-To: <20230509204801.2824351-1-quic_eberman@quicinc.com>
References: <20230509204801.2824351-1-quic_eberman@quicinc.com>
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Gunyah allows host virtual machines to schedule guest virtual machines
and handle their MMIO accesses. vCPUs are presented to the host as a
Gunyah resource and represented to userspace as a Gunyah VM function.

Creating the vcpu VM function will create a file descriptor that:
 - can run an ioctl: GH_VCPU_RUN to schedule the guest vCPU until the
   next interrupt occurs on the host or when the guest vCPU can no
   longer be run.
 - can be mmap'd to share a gh_vcpu_run structure which can look up the
   reason why GH_VCPU_RUN returned and provide return values for MMIO
   access.

Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
---
 Documentation/virt/gunyah/vm-manager.rst |  46 ++-
 arch/arm64/gunyah/gunyah_hypercall.c     |  28 ++
 drivers/virt/gunyah/Kconfig              |  11 +
 drivers/virt/gunyah/Makefile             |   2 +
 drivers/virt/gunyah/gunyah_vcpu.c        | 468 +++++++++++++++++++++++
 drivers/virt/gunyah/vm_mgr.c             |   4 +
 drivers/virt/gunyah/vm_mgr.h             |   1 +
 include/linux/gunyah.h                   |  24 ++
 include/uapi/linux/gunyah.h              | 128 +++++++
 9 files changed, 710 insertions(+), 2 deletions(-)
 create mode 100644 drivers/virt/gunyah/gunyah_vcpu.c

diff --git a/Documentation/virt/gunyah/vm-manager.rst b/Documentation/virt/gunyah/vm-manager.rst
index 3b51bab9d793..6789d13fed14 100644
--- a/Documentation/virt/gunyah/vm-manager.rst
+++ b/Documentation/virt/gunyah/vm-manager.rst
@@ -5,8 +5,7 @@ Virtual Machine Manager
 =======================
 
 The Gunyah Virtual Machine Manager is a Linux driver to support launching
-virtual machines using Gunyah. It presently supports launching non-proxy
-scheduled Linux-like virtual machines.
+virtual machines using Gunyah.
 
 Except for some basic information about the location of initial binaries,
 most of the configuration about a Gunyah virtual machine is described in the
@@ -98,3 +97,46 @@ GH_VM_START
 ~~~~~~~~~~~
 
 This ioctl starts the VM.
+
+GH_VM_ADD_FUNCTION
+~~~~~~~~~~~~~~~~~~
+
+This ioctl registers a Gunyah VM function with the VM manager. The VM function
+is described with a &struct gh_fn_desc.type and some arguments for that type.
+Typically, the function is added before the VM starts, but the function doesn't
+"operate" until the VM starts with `GH_VM_START`_. For example, vCPU ioclts will
+all return an error until the VM starts because the vCPUs don't exist until the
+VM is started. This allows the VMM to set up all the kernel functions needed for
+the VM *before* the VM starts.
+
+.. kernel-doc:: include/uapi/linux/gunyah.h
+   :identifiers: gh_fn_desc gh_fn_type
+
+The argument types are documented below:
+
+.. kernel-doc:: include/uapi/linux/gunyah.h
+   :identifiers: gh_fn_vcpu_arg
+
+Gunyah VCPU API Descriptions
+----------------------------
+
+A vCPU file descriptor is created after calling `GH_VM_ADD_FUNCTION` with the type `GH_FN_VCPU`.
+
+GH_VCPU_RUN
+~~~~~~~~~~~
+
+This ioctl is used to run a guest virtual cpu.  While there are no
+explicit parameters, there is an implicit parameter block that can be
+obtained by mmap()ing the vcpu fd at offset 0, with the size given by
+`GH_VCPU_MMAP_SIZE`_. The parameter block is formatted as a 'struct
+gh_vcpu_run' (see below).
+
+GH_VCPU_MMAP_SIZE
+~~~~~~~~~~~~~~~~~
+
+The `GH_VCPU_RUN`_ ioctl communicates with userspace via a shared
+memory region. This ioctl returns the size of that region. See the
+`GH_VCPU_RUN`_ documentation for details.
+
+.. kernel-doc:: include/uapi/linux/gunyah.h
+   :identifiers: gh_vcpu_exit gh_vcpu_run gh_vm_status gh_vm_exit_info
diff --git a/arch/arm64/gunyah/gunyah_hypercall.c b/arch/arm64/gunyah/gunyah_hypercall.c
index 2b2a63e9b9e5..5f33f53e05a9 100644
--- a/arch/arm64/gunyah/gunyah_hypercall.c
+++ b/arch/arm64/gunyah/gunyah_hypercall.c
@@ -35,6 +35,7 @@ EXPORT_SYMBOL_GPL(arch_is_gh_guest);
 #define GH_HYPERCALL_HYP_IDENTIFY		GH_HYPERCALL(0x8000)
 #define GH_HYPERCALL_MSGQ_SEND			GH_HYPERCALL(0x801B)
 #define GH_HYPERCALL_MSGQ_RECV			GH_HYPERCALL(0x801C)
+#define GH_HYPERCALL_VCPU_RUN			GH_HYPERCALL(0x8065)
 
 /**
  * gh_hypercall_hyp_identify() - Returns build information and feature flags
@@ -83,5 +84,32 @@ enum gh_error gh_hypercall_msgq_recv(u64 capid, void *buff, size_t size, size_t
 }
 EXPORT_SYMBOL_GPL(gh_hypercall_msgq_recv);
 
+enum gh_error gh_hypercall_vcpu_run(u64 capid, u64 *resume_data,
+					struct gh_hypercall_vcpu_run_resp *resp)
+{
+	struct arm_smccc_1_2_regs args = {
+		.a0 = GH_HYPERCALL_VCPU_RUN,
+		.a1 = capid,
+		.a2 = resume_data[0],
+		.a3 = resume_data[1],
+		.a4 = resume_data[2],
+		/* C language says this will be implictly zero. Gunyah requires 0, so be explicit */
+		.a5 = 0,
+	};
+	struct arm_smccc_1_2_regs res;
+
+	arm_smccc_1_2_hvc(&args, &res);
+
+	if (res.a0 == GH_ERROR_OK) {
+		resp->sized_state = res.a1;
+		resp->state_data[0] = res.a2;
+		resp->state_data[1] = res.a3;
+		resp->state_data[2] = res.a4;
+	}
+
+	return res.a0;
+}
+EXPORT_SYMBOL_GPL(gh_hypercall_vcpu_run);
+
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("Gunyah Hypervisor Hypercalls");
diff --git a/drivers/virt/gunyah/Kconfig b/drivers/virt/gunyah/Kconfig
index 0421b751aad4..0a58395f7d2c 100644
--- a/drivers/virt/gunyah/Kconfig
+++ b/drivers/virt/gunyah/Kconfig
@@ -28,3 +28,14 @@ config GUNYAH_QCOM_PLATFORM
 	  extra platform-specific support.
 
 	  Say Y/M here to use Gunyah on Qualcomm platforms.
+
+config GUNYAH_VCPU
+	tristate "Runnable Gunyah vCPUs"
+	depends on GUNYAH
+	help
+	  Enable kernel support for host-scheduled vCPUs running under Gunyah.
+	  When selecting this option, userspace virtual machine managers (VMM)
+	  can schedule the guest VM's vCPUs instead of using Gunyah's scheduler.
+	  VMMs can also handle stage 2 faults of the vCPUs.
+
+	  Say Y/M here if unsure and you want to support Gunyah VMMs.
diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
index 2aa9ff038ed0..cc16b6c19db9 100644
--- a/drivers/virt/gunyah/Makefile
+++ b/drivers/virt/gunyah/Makefile
@@ -5,3 +5,5 @@ obj-$(CONFIG_GUNYAH_QCOM_PLATFORM) += gunyah_qcom.o
 
 gunyah-y += rsc_mgr.o rsc_mgr_rpc.o vm_mgr.o vm_mgr_mm.o
 obj-$(CONFIG_GUNYAH) += gunyah.o
+
+obj-$(CONFIG_GUNYAH_VCPU) += gunyah_vcpu.o
diff --git a/drivers/virt/gunyah/gunyah_vcpu.c b/drivers/virt/gunyah/gunyah_vcpu.c
new file mode 100644
index 000000000000..4f0bbd58a205
--- /dev/null
+++ b/drivers/virt/gunyah/gunyah_vcpu.c
@@ -0,0 +1,468 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/anon_inodes.h>
+#include <linux/file.h>
+#include <linux/gunyah.h>
+#include <linux/gunyah_vm_mgr.h>
+#include <linux/interrupt.h>
+#include <linux/kref.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/wait.h>
+
+#include "vm_mgr.h"
+
+#include <uapi/linux/gunyah.h>
+
+#define MAX_VCPU_NAME		20 /* gh-vcpu:u32_max+NUL */
+
+struct gh_vcpu {
+	struct gh_vm_function_instance *f;
+	struct gh_resource *rsc;
+	struct mutex run_lock;
+	/* Track why vcpu_run left last time around. */
+	enum {
+		GH_VCPU_UNKNOWN = 0,
+		GH_VCPU_READY,
+		GH_VCPU_MMIO_READ,
+		GH_VCPU_SYSTEM_DOWN,
+	} state;
+	u8 mmio_read_len;
+	struct gh_vcpu_run *vcpu_run;
+	struct completion ready;
+	struct gh_vm *ghvm;
+
+	struct notifier_block nb;
+	struct gh_vm_resource_ticket ticket;
+	struct kref kref;
+};
+
+static void vcpu_release(struct kref *kref)
+{
+	struct gh_vcpu *vcpu = container_of(kref, struct gh_vcpu, kref);
+
+	free_page((unsigned long)vcpu->vcpu_run);
+	kfree(vcpu);
+}
+
+/*
+ * When hypervisor allows us to schedule vCPU again, it gives us an interrupt
+ */
+static irqreturn_t gh_vcpu_irq_handler(int irq, void *data)
+{
+	struct gh_vcpu *vcpu = data;
+
+	complete(&vcpu->ready);
+	return IRQ_HANDLED;
+}
+
+static bool gh_handle_mmio(struct gh_vcpu *vcpu,
+				struct gh_hypercall_vcpu_run_resp *vcpu_run_resp)
+{
+	int ret = 0;
+	u64 addr = vcpu_run_resp->state_data[0],
+	    len  = vcpu_run_resp->state_data[1],
+	    data = vcpu_run_resp->state_data[2];
+
+	if (WARN_ON(len > sizeof(u64)))
+		len = sizeof(u64);
+
+	if (vcpu_run_resp->state == GH_VCPU_ADDRSPACE_VMMIO_READ) {
+		vcpu->vcpu_run->mmio.is_write = 0;
+		/* Record that we need to give vCPU user's supplied value next gh_vcpu_run() */
+		vcpu->state = GH_VCPU_MMIO_READ;
+		vcpu->mmio_read_len = len;
+	} else { /* GH_VCPU_ADDRSPACE_VMMIO_WRITE */
+		/* Try internal handlers first */
+		ret = gh_vm_mmio_write(vcpu->f->ghvm, addr, len, data);
+		if (!ret)
+			return true;
+
+		/* Give userspace the info */
+		vcpu->vcpu_run->mmio.is_write = 1;
+		memcpy(vcpu->vcpu_run->mmio.data, &data, len);
+	}
+
+	vcpu->vcpu_run->mmio.phys_addr = addr;
+	vcpu->vcpu_run->mmio.len = len;
+	vcpu->vcpu_run->exit_reason = GH_VCPU_EXIT_MMIO;
+
+	return false;
+}
+
+static int gh_vcpu_rm_notification(struct notifier_block *nb, unsigned long action, void *data)
+{
+	struct gh_vcpu *vcpu = container_of(nb, struct gh_vcpu, nb);
+	struct gh_rm_vm_exited_payload *exit_payload = data;
+
+	if (action == GH_RM_NOTIFICATION_VM_EXITED &&
+		le16_to_cpu(exit_payload->vmid) == vcpu->ghvm->vmid)
+		complete(&vcpu->ready);
+
+	return NOTIFY_OK;
+}
+
+static inline enum gh_vm_status remap_vm_status(enum gh_rm_vm_status rm_status)
+{
+	switch (rm_status) {
+	case GH_RM_VM_STATUS_INIT_FAILED:
+		return GH_VM_STATUS_LOAD_FAILED;
+	case GH_RM_VM_STATUS_EXITED:
+		return GH_VM_STATUS_EXITED;
+	default:
+		return GH_VM_STATUS_CRASHED;
+	}
+}
+
+/**
+ * gh_vcpu_check_system() - Check whether VM as a whole is running
+ * @vcpu: Pointer to gh_vcpu
+ *
+ * Returns true if the VM is alive.
+ * Returns false if the vCPU is the VM is not alive (can only be that VM is shutting down).
+ */
+static bool gh_vcpu_check_system(struct gh_vcpu *vcpu)
+	__must_hold(&vcpu->run_lock)
+{
+	bool ret = true;
+
+	down_read(&vcpu->ghvm->status_lock);
+	if (likely(vcpu->ghvm->vm_status == GH_RM_VM_STATUS_RUNNING))
+		goto out;
+
+	vcpu->vcpu_run->status.status = remap_vm_status(vcpu->ghvm->vm_status);
+	vcpu->vcpu_run->status.exit_info = vcpu->ghvm->exit_info;
+	vcpu->vcpu_run->exit_reason = GH_VCPU_EXIT_STATUS;
+	vcpu->state = GH_VCPU_SYSTEM_DOWN;
+	ret = false;
+out:
+	up_read(&vcpu->ghvm->status_lock);
+	return ret;
+}
+
+/**
+ * gh_vcpu_run() - Request Gunyah to begin scheduling this vCPU.
+ * @vcpu: The client descriptor that was obtained via gh_vcpu_alloc()
+ */
+static int gh_vcpu_run(struct gh_vcpu *vcpu)
+{
+	struct gh_hypercall_vcpu_run_resp vcpu_run_resp;
+	u64 state_data[3] = { 0 };
+	enum gh_error gh_error;
+	int ret = 0;
+
+	if (!vcpu->f)
+		return -ENODEV;
+
+	if (mutex_lock_interruptible(&vcpu->run_lock))
+		return -ERESTARTSYS;
+
+	if (!vcpu->rsc) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	switch (vcpu->state) {
+	case GH_VCPU_UNKNOWN:
+		if (vcpu->ghvm->vm_status != GH_RM_VM_STATUS_RUNNING) {
+			/* Check if VM is up. If VM is starting, will block until VM is fully up
+			 * since that thread does down_write.
+			 */
+			if (!gh_vcpu_check_system(vcpu))
+				goto out;
+		}
+		vcpu->state = GH_VCPU_READY;
+		break;
+	case GH_VCPU_MMIO_READ:
+		if (unlikely(vcpu->mmio_read_len > sizeof(state_data[0])))
+			vcpu->mmio_read_len = sizeof(state_data[0]);
+		memcpy(&state_data[0], vcpu->vcpu_run->mmio.data, vcpu->mmio_read_len);
+		vcpu->state = GH_VCPU_READY;
+		break;
+	case GH_VCPU_SYSTEM_DOWN:
+		goto out;
+	default:
+		break;
+	}
+
+	while (!ret && !signal_pending(current)) {
+		if (vcpu->vcpu_run->immediate_exit) {
+			ret = -EINTR;
+			goto out;
+		}
+
+		gh_error = gh_hypercall_vcpu_run(vcpu->rsc->capid, state_data, &vcpu_run_resp);
+		if (gh_error == GH_ERROR_OK) {
+			switch (vcpu_run_resp.state) {
+			case GH_VCPU_STATE_READY:
+				if (need_resched())
+					schedule();
+				break;
+			case GH_VCPU_STATE_POWERED_OFF:
+				/* vcpu might be off because the VM is shut down.
+				 * If so, it won't ever run again: exit back to user
+				 */
+				if (!gh_vcpu_check_system(vcpu))
+					goto out;
+				/* Otherwise, another vcpu will turn it on (e.g. by PSCI)
+				 * and hyp sends an interrupt to wake Linux up.
+				 */
+				fallthrough;
+			case GH_VCPU_STATE_EXPECTS_WAKEUP:
+				ret = wait_for_completion_interruptible(&vcpu->ready);
+				/* reinitialize completion before next hypercall. If we reinitialize
+				 * after the hypercall, interrupt may have already come before
+				 * re-initializing the completion and then end up waiting for
+				 * event that already happened.
+				 */
+				reinit_completion(&vcpu->ready);
+				/* Check system status again. Completion might've
+				 * come from gh_vcpu_rm_notification
+				 */
+				if (!ret && !gh_vcpu_check_system(vcpu))
+					goto out;
+				break;
+			case GH_VCPU_STATE_BLOCKED:
+				schedule();
+				break;
+			case GH_VCPU_ADDRSPACE_VMMIO_READ:
+			case GH_VCPU_ADDRSPACE_VMMIO_WRITE:
+				if (!gh_handle_mmio(vcpu, &vcpu_run_resp))
+					goto out;
+				break;
+			default:
+				pr_warn_ratelimited("Unknown vCPU state: %llx\n",
+							vcpu_run_resp.sized_state);
+				schedule();
+				break;
+			}
+		} else if (gh_error == GH_ERROR_RETRY) {
+			schedule();
+		} else {
+			ret = gh_error_remap(gh_error);
+		}
+	}
+
+out:
+	mutex_unlock(&vcpu->run_lock);
+
+	if (signal_pending(current))
+		return -ERESTARTSYS;
+
+	return ret;
+}
+
+static long gh_vcpu_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	struct gh_vcpu *vcpu = filp->private_data;
+	long ret = -EINVAL;
+
+	switch (cmd) {
+	case GH_VCPU_RUN:
+		ret = gh_vcpu_run(vcpu);
+		break;
+	case GH_VCPU_MMAP_SIZE:
+		ret = PAGE_SIZE;
+		break;
+	default:
+		break;
+	}
+	return ret;
+}
+
+static int gh_vcpu_release(struct inode *inode, struct file *filp)
+{
+	struct gh_vcpu *vcpu = filp->private_data;
+
+	gh_vm_put(vcpu->ghvm);
+	kref_put(&vcpu->kref, vcpu_release);
+	return 0;
+}
+
+static vm_fault_t gh_vcpu_fault(struct vm_fault *vmf)
+{
+	struct gh_vcpu *vcpu = vmf->vma->vm_file->private_data;
+	struct page *page = NULL;
+
+	if (vmf->pgoff == 0)
+		page = virt_to_page(vcpu->vcpu_run);
+
+	get_page(page);
+	vmf->page = page;
+	return 0;
+}
+
+static const struct vm_operations_struct gh_vcpu_ops = {
+	.fault = gh_vcpu_fault,
+};
+
+static int gh_vcpu_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	vma->vm_ops = &gh_vcpu_ops;
+	return 0;
+}
+
+static const struct file_operations gh_vcpu_fops = {
+	.owner = THIS_MODULE,
+	.unlocked_ioctl = gh_vcpu_ioctl,
+	.release = gh_vcpu_release,
+	.llseek = noop_llseek,
+	.mmap = gh_vcpu_mmap,
+};
+
+static bool gh_vcpu_populate(struct gh_vm_resource_ticket *ticket, struct gh_resource *ghrsc)
+{
+	struct gh_vcpu *vcpu = container_of(ticket, struct gh_vcpu, ticket);
+	int ret;
+
+	mutex_lock(&vcpu->run_lock);
+	if (vcpu->rsc) {
+		pr_warn("vcpu%d already got a Gunyah resource. Check if multiple resources with same label were configured.\n",
+			vcpu->ticket.label);
+		ret = -EEXIST;
+		goto out;
+	}
+
+	vcpu->rsc = ghrsc;
+	init_completion(&vcpu->ready);
+
+	ret = request_irq(vcpu->rsc->irq, gh_vcpu_irq_handler, IRQF_TRIGGER_RISING, "gh_vcpu",
+			vcpu);
+	if (ret)
+		pr_warn("Failed to request vcpu irq %d: %d", vcpu->rsc->irq, ret);
+
+out:
+	mutex_unlock(&vcpu->run_lock);
+	return !ret;
+}
+
+static void gh_vcpu_unpopulate(struct gh_vm_resource_ticket *ticket,
+				   struct gh_resource *ghrsc)
+{
+	struct gh_vcpu *vcpu = container_of(ticket, struct gh_vcpu, ticket);
+
+	vcpu->vcpu_run->immediate_exit = true;
+	complete_all(&vcpu->ready);
+	mutex_lock(&vcpu->run_lock);
+	free_irq(vcpu->rsc->irq, vcpu);
+	vcpu->rsc = NULL;
+	mutex_unlock(&vcpu->run_lock);
+}
+
+static long gh_vcpu_bind(struct gh_vm_function_instance *f)
+{
+	struct gh_fn_vcpu_arg *arg = f->argp;
+	struct gh_vcpu *vcpu;
+	char name[MAX_VCPU_NAME];
+	struct file *file;
+	struct page *page;
+	int fd;
+	long r;
+
+	if (f->arg_size != sizeof(*arg))
+		return -EINVAL;
+
+	vcpu = kzalloc(sizeof(*vcpu), GFP_KERNEL);
+	if (!vcpu)
+		return -ENOMEM;
+
+	vcpu->f = f;
+	f->data = vcpu;
+	mutex_init(&vcpu->run_lock);
+	kref_init(&vcpu->kref);
+
+	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	if (!page) {
+		r = -ENOMEM;
+		goto err_destroy_vcpu;
+	}
+	vcpu->vcpu_run = page_address(page);
+
+	vcpu->ticket.resource_type = GH_RESOURCE_TYPE_VCPU;
+	vcpu->ticket.label = arg->id;
+	vcpu->ticket.owner = THIS_MODULE;
+	vcpu->ticket.populate = gh_vcpu_populate;
+	vcpu->ticket.unpopulate = gh_vcpu_unpopulate;
+
+	r = gh_vm_add_resource_ticket(f->ghvm, &vcpu->ticket);
+	if (r)
+		goto err_destroy_page;
+
+	if (!gh_vm_get(f->ghvm)) {
+		r = -ENODEV;
+		goto err_remove_resource_ticket;
+	}
+	vcpu->ghvm = f->ghvm;
+
+	vcpu->nb.notifier_call = gh_vcpu_rm_notification;
+	/* Ensure we run after the vm_mgr handles the notification and does
+	 * any necessary state changes. We wake up to check the new state.
+	 */
+	vcpu->nb.priority = -1;
+	r = gh_rm_notifier_register(f->rm, &vcpu->nb);
+	if (r)
+		goto err_put_gh_vm;
+
+	kref_get(&vcpu->kref);
+
+	fd = get_unused_fd_flags(O_CLOEXEC);
+	if (fd < 0) {
+		r = fd;
+		goto err_notifier;
+	}
+
+	snprintf(name, sizeof(name), "gh-vcpu:%u", vcpu->ticket.label);
+	file = anon_inode_getfile(name, &gh_vcpu_fops, vcpu, O_RDWR);
+	if (IS_ERR(file)) {
+		r = PTR_ERR(file);
+		goto err_put_fd;
+	}
+
+	fd_install(fd, file);
+
+	return fd;
+err_put_fd:
+	put_unused_fd(fd);
+err_notifier:
+	gh_rm_notifier_unregister(f->rm, &vcpu->nb);
+err_put_gh_vm:
+	gh_vm_put(vcpu->ghvm);
+err_remove_resource_ticket:
+	gh_vm_remove_resource_ticket(f->ghvm, &vcpu->ticket);
+err_destroy_page:
+	free_page((unsigned long)vcpu->vcpu_run);
+err_destroy_vcpu:
+	kfree(vcpu);
+	return r;
+}
+
+static void gh_vcpu_unbind(struct gh_vm_function_instance *f)
+{
+	struct gh_vcpu *vcpu = f->data;
+
+	gh_rm_notifier_unregister(f->rm, &vcpu->nb);
+	gh_vm_remove_resource_ticket(vcpu->f->ghvm, &vcpu->ticket);
+	vcpu->f = NULL;
+
+	kref_put(&vcpu->kref, vcpu_release);
+}
+
+static bool gh_vcpu_compare(const struct gh_vm_function_instance *f,
+				const void *arg, size_t size)
+{
+	const struct gh_fn_vcpu_arg *instance = f->argp,
+					 *other = arg;
+
+	if (sizeof(*other) != size)
+		return false;
+
+	return instance->id == other->id;
+}
+
+DECLARE_GH_VM_FUNCTION_INIT(vcpu, GH_FN_VCPU, 1, gh_vcpu_bind, gh_vcpu_unbind, gh_vcpu_compare);
+MODULE_DESCRIPTION("Gunyah vCPU Function");
+MODULE_LICENSE("GPL");
diff --git a/drivers/virt/gunyah/vm_mgr.c b/drivers/virt/gunyah/vm_mgr.c
index 81b42ab675f6..e7844204c151 100644
--- a/drivers/virt/gunyah/vm_mgr.c
+++ b/drivers/virt/gunyah/vm_mgr.c
@@ -408,6 +408,10 @@ static int gh_vm_rm_notification_exited(struct gh_vm *ghvm, void *data)
 
 	down_write(&ghvm->status_lock);
 	ghvm->vm_status = GH_RM_VM_STATUS_EXITED;
+	ghvm->exit_info.type = le16_to_cpu(payload->exit_type);
+	ghvm->exit_info.reason_size = le32_to_cpu(payload->exit_reason_size);
+	memcpy(&ghvm->exit_info.reason, payload->exit_reason,
+		min(GH_VM_MAX_EXIT_REASON_SIZE, ghvm->exit_info.reason_size));
 	up_write(&ghvm->status_lock);
 	wake_up(&ghvm->vm_status_wait);
 
diff --git a/drivers/virt/gunyah/vm_mgr.h b/drivers/virt/gunyah/vm_mgr.h
index 3fc0f91dfd1a..fa2a61e10b57 100644
--- a/drivers/virt/gunyah/vm_mgr.h
+++ b/drivers/virt/gunyah/vm_mgr.h
@@ -45,6 +45,7 @@ struct gh_vm {
 	enum gh_rm_vm_status vm_status;
 	wait_queue_head_t vm_status_wait;
 	struct rw_semaphore status_lock;
+	struct gh_vm_exit_info exit_info;
 
 	struct work_struct free_work;
 	struct kref kref;
diff --git a/include/linux/gunyah.h b/include/linux/gunyah.h
index 4b398b59c2c5..cd5704a82c6a 100644
--- a/include/linux/gunyah.h
+++ b/include/linux/gunyah.h
@@ -177,4 +177,28 @@ enum gh_error gh_hypercall_msgq_send(u64 capid, size_t size, void *buff, u64 tx_
 enum gh_error gh_hypercall_msgq_recv(u64 capid, void *buff, size_t size, size_t *recv_size,
 					bool *ready);
 
+struct gh_hypercall_vcpu_run_resp {
+	union {
+		enum {
+			/* VCPU is ready to run */
+			GH_VCPU_STATE_READY		= 0,
+			/* VCPU is sleeping until an interrupt arrives */
+			GH_VCPU_STATE_EXPECTS_WAKEUP	= 1,
+			/* VCPU is powered off */
+			GH_VCPU_STATE_POWERED_OFF	= 2,
+			/* VCPU is blocked in EL2 for unspecified reason */
+			GH_VCPU_STATE_BLOCKED		= 3,
+			/* VCPU has returned for MMIO READ */
+			GH_VCPU_ADDRSPACE_VMMIO_READ	= 4,
+			/* VCPU has returned for MMIO WRITE */
+			GH_VCPU_ADDRSPACE_VMMIO_WRITE	= 5,
+		} state;
+		u64 sized_state;
+	};
+	u64 state_data[3];
+};
+
+enum gh_error gh_hypercall_vcpu_run(u64 capid, u64 *resume_data,
+					struct gh_hypercall_vcpu_run_resp *resp);
+
 #endif
diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
index bb07118a351f..434ffa8ffc78 100644
--- a/include/uapi/linux/gunyah.h
+++ b/include/uapi/linux/gunyah.h
@@ -72,8 +72,33 @@ struct gh_vm_dtb_config {
 
 #define GH_VM_START		_IO(GH_IOCTL_TYPE, 0x3)
 
+/**
+ * enum gh_fn_type - Valid types of Gunyah VM functions
+ * @GH_FN_VCPU: create a vCPU instance to control a vCPU
+ *              &struct gh_fn_desc.arg is a pointer to &struct gh_fn_vcpu_arg
+ *              Return: file descriptor to manipulate the vcpu.
+ */
+enum gh_fn_type {
+	GH_FN_VCPU = 1,
+};
+
 #define GH_FN_MAX_ARG_SIZE		256
 
+/**
+ * struct gh_fn_vcpu_arg - Arguments to create a vCPU.
+ * @id: vcpu id
+ *
+ * Create this function with &GH_VM_ADD_FUNCTION using type &GH_FN_VCPU.
+ *
+ * The vcpu type will register with the VM Manager to expect to control
+ * vCPU number `vcpu_id`. It returns a file descriptor allowing interaction with
+ * the vCPU. See the Gunyah vCPU API description sections for interacting with
+ * the Gunyah vCPU file descriptors.
+ */
+struct gh_fn_vcpu_arg {
+	__u32 id;
+};
+
 /**
  * struct gh_fn_desc - Arguments to create a VM function
  * @type: Type of the function. See &enum gh_fn_type.
@@ -90,4 +115,107 @@ struct gh_fn_desc {
 #define GH_VM_ADD_FUNCTION	_IOW(GH_IOCTL_TYPE, 0x4, struct gh_fn_desc)
 #define GH_VM_REMOVE_FUNCTION	_IOW(GH_IOCTL_TYPE, 0x7, struct gh_fn_desc)
 
+/*
+ * ioctls for vCPU fds
+ */
+
+/**
+ * enum gh_vm_status - Stores status reason why VM is not runnable (exited).
+ * @GH_VM_STATUS_LOAD_FAILED: VM didn't start because it couldn't be loaded.
+ * @GH_VM_STATUS_EXITED: VM requested shutdown/reboot.
+ *                       Use &struct gh_vm_exit_info.reason for further details.
+ * @GH_VM_STATUS_CRASHED: VM state is unknown and has crashed.
+ */
+enum gh_vm_status {
+	GH_VM_STATUS_LOAD_FAILED	= 1,
+	GH_VM_STATUS_EXITED		= 2,
+	GH_VM_STATUS_CRASHED		= 3,
+};
+
+/*
+ * Gunyah presently sends max 4 bytes of exit_reason.
+ * If that changes, this macro can be safely increased without breaking
+ * userspace so long as struct gh_vcpu_run < PAGE_SIZE.
+ */
+#define GH_VM_MAX_EXIT_REASON_SIZE	8u
+
+/**
+ * struct gh_vm_exit_info - Reason for VM exit as reported by Gunyah
+ * See Gunyah documentation for values.
+ * @type: Describes how VM exited
+ * @padding: padding bytes
+ * @reason_size: Number of bytes valid for `reason`
+ * @reason: See Gunyah documentation for interpretation. Note: these values are
+ *          not interpreted by Linux and need to be converted from little-endian
+ *          as applicable.
+ */
+struct gh_vm_exit_info {
+	__u16 type;
+	__u16 padding;
+	__u32 reason_size;
+	__u8 reason[GH_VM_MAX_EXIT_REASON_SIZE];
+};
+
+/**
+ * enum gh_vcpu_exit - Stores reason why &GH_VCPU_RUN ioctl recently exited with status 0
+ * @GH_VCPU_EXIT_UNKNOWN: Not used, status != 0
+ * @GH_VCPU_EXIT_MMIO: vCPU performed a read or write that could not be handled
+ *                     by hypervisor or Linux. Use @struct gh_vcpu_run.mmio for
+ *                     details of the read/write.
+ * @GH_VCPU_EXIT_STATUS: vCPU not able to run because the VM has exited.
+ *                       Use @struct gh_vcpu_run.status for why VM has exited.
+ */
+enum gh_vcpu_exit {
+	GH_VCPU_EXIT_UNKNOWN,
+	GH_VCPU_EXIT_MMIO,
+	GH_VCPU_EXIT_STATUS,
+};
+
+/**
+ * struct gh_vcpu_run - Application code obtains a pointer to the gh_vcpu_run
+ *                      structure by mmap()ing a vcpu fd.
+ * @immediate_exit: polled when scheduling the vcpu. If set, immediately returns -EINTR.
+ * @padding: padding bytes
+ * @exit_reason: Set when GH_VCPU_RUN returns successfully and gives reason why
+ *               GH_VCPU_RUN has stopped running the vCPU. See &enum gh_vcpu_exit.
+ * @mmio: Used when exit_reason == GH_VCPU_EXIT_MMIO
+ *        The guest has faulted on an memory-mapped I/O instruction that
+ *        couldn't be satisfied by gunyah.
+ * @mmio.phys_addr: Address guest tried to access
+ * @mmio.data: the value that was written if `is_write == 1`. Filled by
+ *        user for reads (`is_write == 0`).
+ * @mmio.len: Length of write. Only the first `len` bytes of `data`
+ *       are considered by Gunyah.
+ * @mmio.is_write: 1 if VM tried to perform a write, 0 for a read
+ * @status: Used when exit_reason == GH_VCPU_EXIT_STATUS.
+ *          The guest VM is no longer runnable. This struct informs why.
+ * @status.status: See &enum gh_vm_status for possible values
+ * @status.exit_info: Used when status == GH_VM_STATUS_EXITED
+ */
+struct gh_vcpu_run {
+	/* in */
+	__u8 immediate_exit;
+	__u8 padding[7];
+
+	/* out */
+	__u32 exit_reason;
+
+	union {
+		struct {
+			__u64 phys_addr;
+			__u8  data[8];
+			__u32 len;
+			__u8  is_write;
+		} mmio;
+
+		struct {
+			enum gh_vm_status status;
+			struct gh_vm_exit_info exit_info;
+		} status;
+	};
+};
+
+#define GH_VCPU_RUN		_IO(GH_IOCTL_TYPE, 0x5)
+#define GH_VCPU_MMAP_SIZE	_IO(GH_IOCTL_TYPE, 0x6)
+
 #endif
-- 
2.40.0