UVM_MAP(9) | Kernel Developer's Manual | UVM_MAP(9)

# NAME

uvm_map — virtual address space management interface

# SYNOPSIS

#include <sys/param.h>
#include <uvm/uvm.h>
int
uvm_map(struct vm_map *map, vaddr_t *startp, vsize_t size, struct uvm_object *uobj, voff_t uoffset, vsize_t align, uvm_flag_t flags);
void
uvm_unmap(struct vm_map *map, vaddr_t start, vaddr_t end);
int
uvm_map_pageable(struct vm_map *map, vaddr_t start, vaddr_t end, bool new_pageable, int lockflags);
bool
uvm_map_checkprot(struct vm_map *map, vaddr_t start, vaddr_t end, vm_prot_t protection);
int
uvm_map_protect(struct vm_map *map, vaddr_t start, vaddr_t end, vm_prot_t new_prot, bool set_max);
int
uvm_map_protect_user(struct lwp *l, vaddr_t start, vaddr_t end, vm_prot_t new_prot);
int
uvm_deallocate(struct vm_map *map, vaddr_t start, vsize_t size);
struct vmspace *
uvmspace_alloc(vaddr_t min, vaddr_t max);
void
uvmspace_exec(struct lwp *l, vaddr_t start, vaddr_t end);
struct vmspace *
uvmspace_fork(struct vmspace *vm);
void
uvmspace_free(struct vmspace *vm);
void
uvmspace_share(struct proc *p1, struct proc *p2);
vaddr_t
uvm_uarea_alloc(void);
void
uvm_uarea_free(vaddr_t uaddr);
vaddr_t
uvm_uarea_system_alloc(void);
void
uvm_uarea_system_free(vaddr_t uaddr);

# DESCRIPTION

The UVM facility for virtual address space management.

# FUNCTIONS

uvm_map() establishes a valid mapping in map map, which must be unlocked. The new mapping has size size, which must be a multiple of `PAGE_SIZE`.
The uobj and uoffset arguments can have four meanings:

- When uobj is `NULL` and uoffset is `UVM_UNKNOWN_OFFSET`, uvm_map() does not use the machine-dependent `PMAP_PREFER` function.
- When uobj is `NULL` and uoffset is any other value, it is used as the hint to `PMAP_PREFER`.
- When uobj is not `NULL` and uoffset is `UVM_UNKNOWN_OFFSET`, uvm_map() finds the offset based upon the virtual address, passed as startp.
- When uobj is not `NULL` and uoffset is any other value, then a regular mapping is performed at this offset. The start address of the map will be returned in startp.

Note that uvm_map() does not add a reference to uobj; it is the caller's responsibility to do so.
align specifies alignment of mapping unless `UVM_FLAG_FIXED` is specified in flags. align must be a power of 2.
flags passed to uvm_map() are typically created using the UVM_MAPFLAG(vm_prot_t prot, vm_prot_t maxprot, vm_inherit_t inh, int advice, int flags) macro, which uses the following values.
The values that prot and maxprot can take are:

UVM_PROT_NONE
  No protection bits.
UVM_PROT_R
  Read.
UVM_PROT_W
  Write.
UVM_PROT_X
  Exec.
UVM_PROT_MASK
  Mask to extraction the protection bits.

Additionally, the following constants for ORed values are available: `UVM_PROT_RW`, `UVM_PROT_RX`, `UVM_PROT_WX` and `UVM_PROT_RWX`.
The values that inh can take are:

UVM_INH_SHARE
  Share the map.
UVM_INH_COPY
  Copy the map.
UVM_INH_NONE
  No inheritance.
UVM_INH_MASK
  Mask to extract inherit flags.

The values that advice can take are:

UVM_ADV_NORMAL
  "Normal" use.
UVM_ADV_RANDOM
  "Random" access likelihood.
UVM_ADV_SEQUENTIAL
  "Sequential" access likelihood.
UVM_ADV_MASK
  Mask to extract the advice flags.

The values that flags can take are:

UVM_FLAG_FIXED
  Attempt to map on the address specified by startp. Otherwise, it is used just as a hint.
UVM_FLAG_OVERLAY
  Establish overlay.
UVM_FLAG_NOMERGE
  Do not merge map entries, if such merge is possible.
UVM_FLAG_COPYONW
  Use copy-on-write i.e. do not fault in the pages immediately.
UVM_FLAG_AMAPPAD
  Used for BSS: allocate larger amap, if extending is likely.
UVM_FLAG_TRYLOCK
  Fail if cannot acquire the lock immediately.
UVM_FLAG_NOWAIT
  Not allowed to sleep. Fail, in such case.
UVM_FLAG_QUANTUM
  Indicates that map entry cannot be split once mapped.
UVM_FLAG_WAITVA
  Sleep until VA space is available, if it is not.
UVM_FLAG_VAONLY
  Unmap only VA space. Used by uvm_unmap().
UVM_FLAG_UNMAP
  Any existing entires in the range for this mapping should be unmapped as part of creating the new mapping. Use of this flag without also specifying `UVM_FLAG_FIXED` is a bug.

The `UVM_MAPFLAG` macro arguments can be combined with an or operator. There are several special purpose macros for checking protection combinations, e.g., the `UVM_PROT_WX`. There are also some additional macros to extract bits from the flags. The `UVM_PROTECTION`, `UVM_INHERIT`, `UVM_MAXPROTECTION` and `UVM_ADVICE` macros return the protection, inheritance, maximum protection, and advice, respectively. uvm_map() returns zero on success or error number otherwise.
uvm_unmap() removes a valid mapping, from start to end, in map map, which must be unlocked.
uvm_map_pageable() changes the pageability of the pages in the range from start to end in map map to new_pageable. uvm_map_pageable() returns zero on success or error number otherwise.
uvm_map_checkprot() checks the protection of the range from start to end in map map against protection. This returns either `true` or `false`.
uvm_map_protect() changes the protection start to end in map map to new_prot, also setting the maximum protection to the region to new_prot if set_max is true. This function returns a standard UVM return value.
uvm_map_protect_user() verifies that the new permissions honor PAX restrictions if applicable and forwards to uvm_map_protect() on passing.
uvm_deallocate() deallocates kernel memory in map map from address start to start + size.
uvmspace_alloc() allocates and returns a new address space, with ranges from min to max.
uvmspace_exec() either reuses the address space of thread l (its process) if there are no other references to it, or creates a new one with uvmspace_alloc(). The range of valid addresses in the address space is reset to start through end.
uvmspace_fork() creates and returns a new address space based upon the vm address space, typically used when allocating an address space for a child process.
uvmspace_free() lowers the reference count on the address space vm, freeing the data structures if there are no other references.
uvmspace_share() causes process p2 to share the address space of p1.
uvm_uarea_alloc() allocates memory for a u-area (i.e. kernel stack, PCB, etc) and returns the address.
uvm_uarea_free() frees a u-area allocated with uvm_uarea_alloc().
uvm_uarea_system_alloc() and uvm_uarea_system_free() are optimized routines, which are used for kernel threads.

# SEE ALSO

pmap(9), uvm(9), uvm_km(9), vmem(9)

# HISTORY

UVM and uvm_map first appeared in NetBSD 1.4.

May 20, 2017 | NetBSD 8.2