104 lines
3.4 KiB
Groff
104 lines
3.4 KiB
Groff
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.\"
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.\" Copyright (c) 2015 Jason A. Harmening <jah@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 6, 2015
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.Dt PMAP_QUICK_ENTER_PAGE 9
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.Os
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.Sh NAME
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.Nm pmap_quick_enter_page ,
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.Nm pmap_quick_remove_page
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.Nd manage fast, single-page kernel address space mappings
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.Sh SYNOPSIS
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.In sys/param.h
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.In vm/vm.h
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.In vm/pmap.h
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.Ft vm_offset_t
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.Fn pmap_quick_enter_page "vm_page_t m"
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.Ft void
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.Fn pmap_quick_remove_page "vm_offset_t kva"
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.Sh DESCRIPTION
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The
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.Fn pmap_quick_enter_page
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function accepts a single page
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.Fa m ,
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and enters this page into a preallocated address in kernel virtual
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address (KVA) space.
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This function is intended for temporary mappings that will only
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be used for a very short period, for example a copy operation on
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the page contents.
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.Pp
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The
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.Fn pmap_quick_remove_page
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function removes a mapping previously created by
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.Fn pmap_quick_enter_page
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at
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.Fa kva ,
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making the KVA frame used by
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.Fn pmap_quick_enter_page
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available for reuse.
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.Pp
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On many architectures,
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.Fn pmap_quick_enter_page
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uses a per-CPU pageframe.
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In those cases, it must disable preemption on the local CPU.
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The corresponding call to
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.Fn pmap_quick_remove_page
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then re-enables preemption.
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It is therefore not safe for machine-independent code to sleep
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or perform locking operations while holding these mappings.
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Current implementations only guarantee the availability of a single
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page for the calling thread, so calls to
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.Fn pmap_quick_enter_page
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must not be nested.
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.Pp
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.Fn pmap_quick_enter_page
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and
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.Fn pmap_quick_remove_page
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do not sleep, and
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.Fn pmap_quick_enter_page
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always returns a valid address.
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It is safe to use these functions under all types of locks except spin mutexes.
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It is also safe to use them in all thread contexts except primary interrupt
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context.
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.Pp
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The page
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.Em must
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not be swapped or otherwise reused while the mapping is active.
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It must be either wired or held, or it must belong to an unmanaged
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region such as I/O device memory.
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.Sh RETURN VALUES
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The
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.Fn pmap_quick_enter_page
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function returns the kernel virtual address
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that is mapped to the page
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.Fa m .
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.Sh SEE ALSO
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.Xr pmap 9
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.Sh AUTHORS
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This manual page was written by
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.An Jason A Harmening Aq Mt jah@FreeBSD.org .
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