LIBNVMM(3) | Library Functions Manual | LIBNVMM(3)

# NAME

`libnvmm` —
NetBSD Virtualization API

# LIBRARY

library “libnvmm”

# SYNOPSIS

`#include <nvmm.h>`

int
`nvmm_init`(void);

int
`nvmm_capability`(struct nvmm_capability *cap);

int
`nvmm_machine_create`(struct nvmm_machine *mach);

int
`nvmm_machine_destroy`(struct nvmm_machine *mach);

int
`nvmm_machine_configure`(struct nvmm_machine *mach, uint64_t op, void *conf);

int
`nvmm_vcpu_create`(struct nvmm_machine *mach, nvmm_cpuid_t cpuid, struct nvmm_vcpu *vcpu);

int
`nvmm_vcpu_destroy`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu);

int
`nvmm_vcpu_configure`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu, uint64_t op, void *conf);

int
`nvmm_vcpu_getstate`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu, uint64_t flags);

int
`nvmm_vcpu_setstate`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu, uint64_t flags);

int
`nvmm_vcpu_inject`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu);

int
`nvmm_vcpu_run`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu);

int
`nvmm_hva_map`(struct nvmm_machine *mach, uintptr_t hva, size_t size);

int
`nvmm_hva_unmap`(struct nvmm_machine *mach, uintptr_t hva, size_t size);

int
`nvmm_gpa_map`(struct nvmm_machine *mach, uintptr_t hva, gpaddr_t gpa, size_t size, int prot);

int
`nvmm_gpa_unmap`(struct nvmm_machine *mach, uintptr_t hva, gpaddr_t gpa, size_t size);

int
`nvmm_gva_to_gpa`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu, gvaddr_t gva, gpaddr_t *gpa, nvmm_prot_t *prot);

int
`nvmm_gpa_to_hva`(struct nvmm_machine *mach, gpaddr_t gpa, uintptr_t *hva, nvmm_prot_t *prot);

int
`nvmm_assist_io`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu);

int
`nvmm_assist_mem`(struct nvmm_machine *mach, struct nvmm_vcpu *vcpu);

# DESCRIPTION

`libnvmm` provides a library for emulator software to handle hardware-accelerated virtual machines in NetBSD. A virtual machine is described by an opaque structure, `nvmm_machine`. Emulator software should not attempt to modify this structure directly, and should use the API provided by `libnvmm` to manage virtual machines. A virtual CPU is described by a public structure, `nvmm_vcpu`.

`nvmm_init`() initializes NVMM. See NVMM Initialization below for details.

`nvmm_capability`() gets the capabilities of NVMM. See NVMM Capability below for details.

`nvmm_machine_create`() creates a virtual machine in the kernel. The mach structure is initialized, and describes the machine.

`nvmm_machine_destroy`() destroys the virtual machine described in mach.

`nvmm_machine_configure`() configures, on the machine mach, the parameter indicated in op. conf describes the value of the parameter.

`nvmm_vcpu_create`() creates a virtual CPU in the machine mach, giving it the CPU id cpuid, and initializes vcpu.

`nvmm_vcpu_destroy`() destroys the virtual CPU identified by vcpu in the machine mach.

`nvmm_vcpu_configure`() configures, on the VCPU vcpu of machine mach, the parameter indicated in op. conf describes the value of the parameter.

`nvmm_vcpu_getstate`() gets the state of the virtual CPU identified by vcpu in the machine mach. flags is the bitmap of the components that are to be retrieved. The components are located in vcpu->state. See VCPU State Area below for details.

`nvmm_vcpu_setstate`() sets the state of the virtual CPU identified by vcpu in the machine mach. flags is the bitmap of the components that are to be set. The components are located in vcpu->state. See VCPU State Area below for details.

`nvmm_vcpu_inject`() injects into the CPU identified by vcpu of the machine mach an event described by vcpu->event. See Event Injection below for details.

`nvmm_vcpu_run`() runs the CPU identified by vcpu in the machine mach, until a VM exit is triggered. The vcpu->exit structure is filled to indicate the exit reason, and the associated parameters if any.

`nvmm_hva_map`() maps at address hva a buffer of size size in the calling process' virtual address space. This buffer is allowed to be subsequently mapped in a virtual machine.

`nvmm_hva_unmap`() unmaps the buffer of size size at address hva from the calling process' virtual address space.

`nvmm_gpa_map`() maps into the guest physical memory beginning on address gpa the buffer of size size located at address hva of the calling process' virtual address space. The hva parameter must point to a buffer that was previously mapped with `nvmm_hva_map`().

`nvmm_gpa_unmap`() removes the guest physical memory area beginning on address gpa and of size size from the machine mach.

`nvmm_gva_to_gpa`() translates, on the CPU vcpu from the machine mach, the guest virtual address given in gva into a guest physical address returned in gpa. The associated page premissions are returned in prot. gva must be page-aligned.

`nvmm_gpa_to_hva`() translates, on the machine mach, the guest physical address indicated in gpa into a host virtual address returned in hva. The associated page premissions are returned in prot. gpa must be page-aligned.

`nvmm_assist_io`() emulates the I/O operation described in vcpu->exit on CPU vcpu from machine mach. See I/O Assist below for details.

`nvmm_assist_mem`() emulates the Mem operation described in vcpu->exit on CPU vcpu from machine mach. See Mem Assist below for details.

## NVMM Initialization

NVMM initialization is performed by the `nvmm_init`() function, which must be invoked by emulator software before any other NVMM function.

`nvmm_init`() opens the NVMM device, and expects to have the proper permissions to do so. In a default configuration, this implies being part of the "nvmm" group. If using a special configuration, emulator software should arrange to have the proper permissions before invoking `nvmm_init`(), and can drop them after the call has completed.

It is to be noted that `nvmm_init`() may perform non-re-entrant operations, and should be called only once.

## NVMM Capability

The `nvmm_capability` structure helps emulator software identify the capabilities offered by NVMM on the host:

    struct nvmm_capability {
    	uint64_t version;
    	uint64_t state_size;
    	uint64_t max_machines;
    	uint64_t max_vcpus;
    	uint64_t max_ram;
    	struct {
    		...
    	} arch;
    };

For example, the `max_machines` field indicates the maximum number of virtual machines supported, while `max_vcpus` indicates the maximum number of VCPUs supported per virtual machine.

## Machine Ownership

When a process creates a virtual machine via `nvmm_machine_create`(), it is considered the owner of this machine. No other processes than the owner can operate a virtual machine.

When an owner exits, all the virtual machines associated with it are destroyed, if they were not already destroyed by the owner itself via `nvmm_machine_destroy`().

Virtual machines are not inherited across fork(2) operations.

## Machine Configuration

Emulator software can configure several parameters of a virtual machine by using `nvmm_machine_configure`(). Currently, no parameters are implemented.

## VCPU Configuration

Emulator software can configure several parameters of a VCPU by using `nvmm_vcpu_configure`(), which can take the following operations:

    #define NVMM_VCPU_CONF_CALLBACKS	0
    	...

The higher fields depend on the architecture.

## Guest-Host Mappings

Each virtual machine has an associated guest physical memory. Emulator software is allowed to modify this guest physical memory by mapping it into some parts of its virtual address space.

Emulator software should follow the following steps to achieve that:

- Call `nvmm_hva_map`() to create in the host's virtual address space an area of memory that can be shared with a guest. Typically, the hva parameter will be a pointer to an area that was previously mapped via `mmap`(). `nvmm_hva_map`() will replace the content of the area, and will make it read-write (but not executable).
- Make available in the guest an area of guest physical memory, by calling `nvmm_gpa_map`() and passing in the hva parameter the value that was previously given to `nvmm_hva_map`(). `nvmm_gpa_map`() does not replace the content of any memory, it only creates a direct link from gpa into hva. `nvmm_gpa_unmap`() removes this link without modifying hva.

The guest will then be able to use the guest physical address passed in the gpa parameter of `nvmm_gpa_map`(). Each change the guest makes in gpa will be reflected in the host's hva, and vice versa.

It is illegal for emulator software to use `munmap`() on an area that was mapped via `nvmm_hva_map`().

## VCPU State Area

A VCPU state area is a structure that entirely defines the content of the registers of a VCPU. Only one such structure exists, for x86:

    struct nvmm_x64_state {
    	struct nvmm_x64_state_seg segs[NVMM_X64_NSEG];
    	uint64_t gprs[NVMM_X64_NGPR];
    	uint64_t crs[NVMM_X64_NCR];
    	uint64_t drs[NVMM_X64_NDR];
    	uint64_t msrs[NVMM_X64_NMSR];
    	struct nvmm_x64_state_intr intr;
    	struct fxsave fpu;
    };
    #define nvmm_vcpu_state nvmm_x64_state

Refer to functional examples to see precisely how to use this structure.

A VCPU state area is divided in sub-states. A flags parameter is used to set and get the VCPU state; it acts as a bitmap which indicates which sub-states to set or get.

During VM exits, a partial VCPU state area is provided in exitstate, see Exit Reasons below for details.

## VCPU Programming Model

A VCPU is described by a public structure, `nvmm_vcpu`:

    struct nvmm_vcpu {
    	nvmm_cpuid_t cpuid;
    	struct nvmm_vcpu_state *state;
    	struct nvmm_vcpu_event *event;
    	struct nvmm_vcpu_exit *exit;
    };

This structure is used both publicly by emulator software and internally by `libnvmm`. Emulator software should not modify the pointers of this structure, because they are initialized to special values by `libnvmm`.

A call to `nvmm_vcpu_getstate`() will fetch the desired parts of the VCPU state and put them in vcpu->state. A call to `nvmm_vcpu_setstate`() will install in the VCPU the desired parts of vcpu->state. A call to `nvmm_vcpu_inject`() will inject in the VCPU the event in vcpu->event. A call to `nvmm_vcpu_run`() will fill vcpu->exit with the VCPU exit information.

If emulator software uses several threads, a VCPU should be associated with only one thread, and only this thread should perform VCPU modifications. Emulator software should not modify the state of a VCPU with several different threads.

## Exit Reasons

The `nvmm_vcpu_exit` structure is used to handle VM exits:

    /* Generic. */
    #define NVMM_VCPU_EXIT_NONE		0x0000000000000000ULL
    #define NVMM_VCPU_EXIT_INVALID		0xFFFFFFFFFFFFFFFFULL
    /* x86: operations. */
    #define NVMM_VCPU_EXIT_MEMORY		0x0000000000000001ULL
    #define NVMM_VCPU_EXIT_IO		0x0000000000000002ULL
    /* x86: changes in VCPU state. */
    #define NVMM_VCPU_EXIT_SHUTDOWN		0x0000000000001000ULL
    #define NVMM_VCPU_EXIT_INT_READY	0x0000000000001001ULL
    #define NVMM_VCPU_EXIT_NMI_READY	0x0000000000001002ULL
    #define NVMM_VCPU_EXIT_HALTED		0x0000000000001003ULL
    #define NVMM_VCPU_EXIT_TPR_CHANGED	0x0000000000001004ULL
    /* x86: instructions. */
    #define NVMM_VCPU_EXIT_RDMSR		0x0000000000002000ULL
    #define NVMM_VCPU_EXIT_WRMSR		0x0000000000002001ULL
    #define NVMM_VCPU_EXIT_MONITOR		0x0000000000002002ULL
    #define NVMM_VCPU_EXIT_MWAIT		0x0000000000002003ULL
    #define NVMM_VCPU_EXIT_CPUID		0x0000000000002004ULL

    struct nvmm_vcpu_exit {
    	uint64_t reason;
    	union {
    		...
    	} u;
    	struct {
    		...
    	} exitstate;
    };

The reason field indicates the reason of the VM exit. Additional parameters describing the exit can be present in u. exitstate contains a partial, implementation-specific VCPU state, usable as a fast-path to retrieve certain state values.

It is possible that a VM exit was caused by a reason internal to the host kernel, and that emulator software should not be concerned with. In this case, the exit reason is set to `NVMM_VCPU_EXIT_NONE`. This gives a chance for emulator software to halt the VM in its tracks.

Refer to functional examples to see precisely how to handle VM exits.

## Event Injection

It is possible to inject an event into a VCPU. An event can be a hardware interrupt, a software interrupt, or a software exception, defined by:

    #define NVMM_VCPU_EVENT_EXCP	0
    #define NVMM_VCPU_EVENT_INTR	1

    struct nvmm_vcpu_event {
    	u_int type;
    	uint8_t vector;
    	union {
    		struct {
    			uint64_t error;
    		} excp;
    	} u;
    };

This describes an event of type type, to be sent to vector number vector, with a possible additional error code that is implementation-specific.

It is possible that the VCPU is in a state where it cannot receive this event, if:

- the event is a hardware interrupt, and the VCPU runs with interrupts disabled, or
- the event is a non-maskable interrupt (NMI), and the VCPU is already in an in-NMI context.

Emulator software can manage interrupt and NMI window-exiting via the intr component of the VCPU state. When such window-exiting is enabled, NVMM will cause a VM exit with reason `NVMM_VCPU_EXIT_INT_READY` or `NVMM_VCPU_EXIT_NMI_READY` to indicate that the guest is now able to handle the corresponding class of interrupts.

## Assist Callbacks

In order to assist emulation of certain operations, `libnvmm` requires emulator software to register, via `nvmm_vcpu_configure`(), a set of callbacks described in the following structure:

    struct nvmm_assist_callbacks {
    	void (*io)(struct nvmm_io *);
    	void (*mem)(struct nvmm_mem *);
    };

These callbacks are used by `libnvmm` each time `nvmm_assist_io`() or `nvmm_assist_mem`() are invoked. Emulator software that does not intend to use either of these assists can put `NULL` in the callbacks.

## I/O Assist

When a VM exit occurs with reason `NVMM_VCPU_EXIT_IO`, it is necessary for emulator software to emulate the associated I/O operation. `libnvmm` provides an easy way for emulator software to perform that.

`nvmm_assist_io`() will call the registered io callback function and give it a `nvmm_io` structure as argument. This structure describes an I/O transaction:

    struct nvmm_io {
    	struct nvmm_machine *mach;
    	struct nvmm_vcpu *vcpu;
    	uint16_t port;
    	bool in;
    	size_t size;
    	uint8_t *data;
    };

The callback can emulate the operation using this descriptor, following two unique cases:

- The operation is an input. In this case, the callback should fill data with the desired value.
- The operation is an output. In this case, the callback should read data to retrieve the desired value.

In either case, port will indicate the I/O port, in will indicate if the operation is an input, and size will indicate the size of the access.

## Mem Assist

When a VM exit occurs with reason `NVMM_VCPU_EXIT_MEMORY`, it is necessary for emulator software to emulate the associated memory operation. `libnvmm` provides an easy way for emulator software to perform that, similar to the I/O Assist.

`nvmm_assist_mem`() will call the registered mem callback function and give it a `nvmm_mem` structure as argument. This structure describes a Mem transaction:

    struct nvmm_mem {
    	struct nvmm_machine *mach;
    	struct nvmm_vcpu *vcpu;
    	gpaddr_t gpa;
    	bool write;
    	size_t size;
    	uint8_t *data;
    };

The callback can emulate the operation using this descriptor, following two unique cases:

- The operation is a read. In this case, the callback should fill data with the desired value.
- The operation is a write. In this case, the callback should read data to retrieve the desired value.

In either case, gpa will indicate the guest physical address, write will indicate if the access is a write, and size will indicate the size of the access.

# RETURN VALUES

Upon successful completion, each of these functions returns zero. Otherwise, a value of -1 is returned and the global variable errno is set to indicate the error.

# FILES

https://www.netbsd.org/~maxv/nvmm/nvmm-demo.zip
  Functional example (demonstrator). Contains an emulator that uses the `libnvmm` API, and a small kernel that exercises this emulator.
src/sys/dev/nvmm/
  Source code of the kernel NVMM driver.
src/lib/libnvmm/
  Source code of the `libnvmm` library.

# ERRORS

These functions will fail if:

[`EEXIST`]
  An attempt was made to create a machine or a VCPU that already exists.
[`EFAULT`]
  An attempt was made to emulate a memory-based operation in a guest, and the guest page tables did not have the permissions necessary for the operation to complete successfully.
[`EINVAL`]
  An inappropriate parameter was used.
[`ENOBUFS`]
  The maximum number of machines or VCPUs was reached.
[`ENOENT`]
  A query was made on a machine or a VCPU that does not exist.
[`EPERM`]
  An attempt was made to access a machine that does not belong to the process.

# SEE ALSO

nvmm(4), nvmmctl(8)

# AUTHORS

NVMM was designed and implemented by Maxime Villard.

February 9, 2020 | NetBSD 9.0