NAME
pmap_quick_enter_page,
pmap_quick_remove_page —
manage fast, single-page kernel address
space mappings
SYNOPSIS
#include
<sys/param.h>
#include <vm/vm.h>
#include <vm/pmap.h>
vm_offset_t
pmap_quick_enter_page(vm_page_t
m);
void
pmap_quick_remove_page(vm_offset_t
kva);
DESCRIPTION
Thepmap_quick_enter_page()
function accepts a single page m, and enters this page
into a preallocated address in kernel virtual address (KVA) space. This
function is intended for temporary mappings that will only be used for a very
short period, for example a copy operation on the page contents.
The
pmap_quick_remove_page()
function removes a mapping previously created by
pmap_quick_enter_page() at
kva, making the KVA frame used by
pmap_quick_enter_page() available for reuse.
On many architectures,
pmap_quick_enter_page()
uses a per-CPU pageframe. In those cases, it must disable preemption on the
local CPU. The corresponding call to
pmap_quick_remove_page() then re-enables preemption.
It is therefore not safe for machine-independent code to sleep or perform
locking operations while holding these mappings. Current implementations
only guarantee the availability of a single page for the calling thread, so
calls to pmap_quick_enter_page() must not be
nested.
pmap_quick_enter_page()
and pmap_quick_remove_page() do not sleep, and
pmap_quick_enter_page() always returns a valid
address. It is safe to use these functions under all types of locks except
spin mutexes. It is also safe to use them in all thread contexts except
primary interrupt context.
The page must not be swapped or otherwise reused while the mapping is active. It must be either wired or held, or it must belong to an unmanaged region such as I/O device memory.
RETURN VALUES
The pmap_quick_enter_page() function
returns the kernel virtual address that is mapped to the page
m.
SEE ALSO
AUTHORS
This manual page was written by Jason A Harmening <jah@FreeBSD.org>.