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.\" Copyright (c) 2015 Jason A. Harmening <jah@FreeBSD.org>
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.Dd August 6, 2015
.Dt PMAP_QUICK_ENTER_PAGE 9
.Os
.Sh NAME
.Nm pmap_quick_enter_page ,
.Nm pmap_quick_remove_page
.Nd manage fast, single-page kernel address space mappings
.Sh SYNOPSIS
.In sys/param.h
.In vm/vm.h
.In vm/pmap.h
.Ft vm_offset_t
.Fn pmap_quick_enter_page "vm_page_t m"
.Ft void
.Fn pmap_quick_remove_page "vm_offset_t kva"
.Sh DESCRIPTION
The
.Fn pmap_quick_enter_page
function accepts a single page
.Fa 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.
.Pp
The
.Fn pmap_quick_remove_page
function removes a mapping previously created by
.Fn pmap_quick_enter_page
at
.Fa kva ,
making the KVA frame used by
.Fn pmap_quick_enter_page
available for reuse.
.Pp
On many architectures,
.Fn pmap_quick_enter_page
uses a per-CPU pageframe.
In those cases, it must disable preemption on the local CPU.
The corresponding call to
.Fn 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
.Fn pmap_quick_enter_page
must not be nested.
.Pp
.Fn pmap_quick_enter_page
and
.Fn pmap_quick_remove_page
do not sleep, and
.Fn 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.
.Pp
The page
.Em 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.
.Sh RETURN VALUES
The
.Fn pmap_quick_enter_page
function returns the kernel virtual address
that is mapped to the page
.Fa m .
.Sh SEE ALSO
.Xr pmap 9
.Sh AUTHORS
This manual page was written by
.An Jason A Harmening Aq Mt jah@FreeBSD.org .
