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zx_vmar_map

NAME

Add a memory mapping.

SYNOPSIS

#include <zircon/syscalls.h>

zx_status_t zx_vmar_map(zx_handle_t handle,
                        zx_vm_option_t options,
                        size_t vmar_offset,
                        zx_handle_t vmo,
                        uint64_t vmo_offset,
                        size_t len,
                        zx_vaddr_t* mapped_addr);

DESCRIPTION

Maps the given VMO into the given virtual memory address region. The mapping retains a reference to the underlying virtual memory object, which means closing the VMO handle does not remove the mapping added by this function.

options is a bit vector of the following:

  • ZX_VM_SPECIFIC Use the vmar_offset to place the mapping, invalid if handle does not have the ZX_VM_CAN_MAP_SPECIFIC permission. vmar_offset is an offset relative to the base address of the given VMAR. It is an error to specify a range that overlaps with another VMAR or mapping.
  • ZX_VM_SPECIFIC_OVERWRITE Same as ZX_VM_SPECIFIC, but can overlap another mapping. It is still an error to partially-overlap another VMAR. If the range meets these requirements, it will atomically (with respect to all other map/unmap/protect operations) replace existing mappings in the range specified by vmar_offset and len. If that range partially overlaps any mappings, then the portions of those mappings outside the range will remain mapped.
  • ZX_VM_PERM_READ Map vmo as readable. It is an error if handle does not have ZX_VM_CAN_MAP_READ permissions, the handle does not have the ZX_RIGHT_READ right, or the vmo handle does not have the ZX_RIGHT_READ right.
  • ZX_VM_PERM_WRITE Map vmo as writable. It is an error if handle does not have ZX_VM_CAN_MAP_WRITE permissions, the handle does not have the ZX_RIGHT_WRITE right, or the vmo handle does not have the ZX_RIGHT_WRITE right.
  • ZX_VM_PERM_EXECUTE Map vmo as executable. It is an error if handle does not have ZX_VM_CAN_MAP_EXECUTE permissions, the handle handle does not have the ZX_RIGHT_EXECUTE right, or the vmo handle does not have the ZX_RIGHT_EXECUTE right.
  • ZX_VM_MAP_RANGE Immediately page into the new mapping all backed regions of the VMO. This cannot be specified if ZX_VM_SPECIFIC_OVERWRITE is used.
  • ZX_VM_ALLOW_FAULTS Required if it would be possible for the created mapping to generate faults. In particular, it is required if vmo is resizable, if vmo is non-resizable but the mapping extends past the end of vmo, or if vmo was created from zx_pager_create_vmo().

vmar_offset must be 0 if options does not have ZX_VM_SPECIFIC or ZX_VM_SPECIFIC_OVERWRITE set. If neither of those are set, then the mapping will be assigned an offset at random by the kernel (with an allocator determined by policy set on the target VMAR).

len must be page-aligned.

In addition one of the following power-of-two alignment flags can added:

  • ZX_VM_ALIGN_1KB aligns child_addr to a power-of-2 at least 1K bytes.
  • ZX_VM_ALIGN_2KB aligns child_addr to a power-of-2 at least 2K bytes.
  • ZX_VM_ALIGN_4KB aligns child_addr to a power-of-2 at least 4K bytes.
  • ZX_VM_ALIGN_8KB aligns child_addr to a power-of-2 at least 8K bytes. and continues up to
  • ZX_VM_ALIGN_4GB aligns child_addr to a power-of-2 at least 4G bytes.

TODO(fxbug.dev/33764): Currently, alignment flags greater than 4KB cannot be used when mapping a VMO into a compact VMAR.

Using ZX_VM_ALIGN flags with ZX_VM_SPECIFIC will fail if the vmar base address + vmo_offset are not aligned to the requested value.

RIGHTS

handle must be of type ZX_OBJ_TYPE_VMAR.

vmo must be of type ZX_OBJ_TYPE_VMO.

RETURN VALUE

zx_vmar_map() returns ZX_OK and the absolute base address of the mapping (via mapped_addr) on success. The base address will be page-aligned and non-zero. In the event of failure, a negative error value is returned.

ERRORS

ZX_ERR_BAD_HANDLE handle or vmo is not a valid handle.

ZX_ERR_WRONG_TYPE handle or vmo is not a VMAR or VMO handle, respectively.

ZX_ERR_BAD_STATE handle refers to a destroyed VMAR.

ZX_ERR_INVALID_ARGS mapped_addr or options are not valid, vmar_offset is non-zero when neither ZX_VM_SPECIFIC nor ZX_VM_SPECIFIC_OVERWRITE are given, ZX_VM_SPECIFIC_OVERWRITE and ZX_VM_MAP_RANGE are both given, vmar_offset and len describe an unsatisfiable allocation due to exceeding the region bounds, vmar_offset or vmo_offset or len are not page-aligned, vmo_offset + ROUNDUP(len, PAGE_SIZE) overflows.

ZX_ERR_ACCESS_DENIED Insufficient privileges to make the requested mapping.

ZX_ERR_NOT_SUPPORTED If the vmo is resizable or backed by a pager but ZX_VM_ALLOW_FAULTS is not set.

ZX_ERR_BUFFER_TOO_SMALL The VMO is not resizable and the mapping extends past the end of the VMO but ZX_VM_ALLOW_FAULTS is not set.

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.

NOTES

The VMO that backs a memory mapping can be resized to a smaller size. This can cause the thread is reading or writing to the VMAR region to fault. To avoid this hazard, services that receive VMOs from clients should use ZX_VM_REQUIRE_NON_RESIZABLE when mapping the VMO.

SEE ALSO