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guest_set_trap.md

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zx_guest_set_trap

SUMMARY

Sets a trap within a guest.

DECLARATION

#include <zircon/syscalls.h>

zx_status_t zx_guest_set_trap(zx_handle_t handle,
                              uint32_t kind,
                              zx_vaddr_t addr,
                              size_t size,
                              zx_handle_t port_handle,
                              uint64_t key);

DESCRIPTION

zx_guest_set_trap() sets a trap within a guest, which generates a packet when there is an access by a VCPU within the address range defined by addr and size, within the address space defined by kind.

kind may be either ZX_GUEST_TRAP_BELL, ZX_GUEST_TRAP_MEM, or ZX_GUEST_TRAP_IO. If ZX_GUEST_TRAP_BELL or ZX_GUEST_TRAP_MEM is specified, then addr and size must both be page-aligned. ZX_GUEST_TRAP_BELL is an asynchronous trap, and both ZX_GUEST_TRAP_MEM and ZX_GUEST_TRAP_IO are synchronous traps.

Packets for synchronous traps will be delivered through zx_vcpu_enter() and packets for asynchronous traps will be delivered through port_handle.

port_handle must be ZX_HANDLE_INVALID for synchronous traps. For asynchronous traps port_handle must be valid and a packet for the trap will be delivered through port_handle each time the trap is triggered. A fixed number of packets are pre-allocated per trap. If all the packets are exhausted, execution of the VCPU that caused the trap will be paused. When at least one packet is dequeued, execution of the VCPU will resume. To dequeue a packet from port_handle, use zx_port_wait(). Multiple threads may use zx_port_wait() to dequeue packets, enabling the use of a thread pool to handle traps.

key is used to set the key field within zx_port_packet_t, and can be used to distinguish between packets for different traps.

ZX_GUEST_TRAP_BELL is a type of trap that defines a door-bell. If there is an access to the memory region specified by the trap, then a packet is generated that does not fetch the instruction associated with the access. The packet will then be delivered asynchronously via port_handle.

To identify what kind of trap generated a packet, use ZX_PKT_TYPE_GUEST_MEM, ZX_PKT_TYPE_GUEST_IO, ZX_PKT_TYPE_GUEST_BELL, and ZX_PKT_TYPE_GUEST_VCPU. ZX_PKT_TYPE_GUEST_VCPU is a special packet, not caused by a trap, that indicates that the guest requested to start an additional VCPU.

RIGHTS

handle must be of type ZX_OBJ_TYPE_GUEST and have ZX_RIGHT_WRITE.

port_handle must be of type ZX_OBJ_TYPE_PORT and have ZX_RIGHT_WRITE.

RETURN VALUE

zx_guest_set_trap() returns ZX_OK on success. On failure, an error value is returned.

ERRORS

ZX_ERR_ACCESS_DENIED handle or port_handle do not have the ZX_RIGHT_WRITE right.

ZX_ERR_ALREADY_EXISTS A trap for kind already exists that intersects with addr and size.

ZX_ERR_BAD_HANDLE handle or port_handle are invalid handles.

ZX_ERR_INVALID_ARGS kind is not a valid address space, or ZX_GUEST_TRAP_MEM was specified with a port_handle.

ZX_ERR_NO_MEMORY Failure due to lack of memory. There is no good way for userspace to handle this (unlikely) error. In a future build this error will no longer occur.

ZX_ERR_OUT_OF_RANGE The region specified by addr and size is outside of of the valid bounds of the address space kind.

ZX_ERR_WRONG_TYPE handle is not a handle to a guest, or port_handle is not a handle to a port.

NOTES

ZX_GUEST_TRAP_BELL shares the same address space as ZX_GUEST_TRAP_MEM.

On x86-64, if kind is ZX_GUEST_TRAP_BELL or ZX_GUEST_TRAP_MEM and addr is the address of the local APIC, then size must be equivalent to the size of a page. This is due to a special page being mapped when a trap is requested at the address of the local APIC. This allows us to take advantage of hardware acceleration when available.

SEE ALSO