docs: man: Add pmap(9) page

Signed-off-by: Ian Moffett <ian@osmora.org>

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+.\" Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions are met:
+.\"
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+.\"    this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
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+.\" 3. Neither the name of Hyra nor the names of its
+.\"    contributors may be used to endorse or promote products derived from
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+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+.\" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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+.\" ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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+.\" POSSIBILITY OF SUCH DAMAGE.
+.Dd Jan 12 2024
+.Dt PMAP 9
+.Os Hyra
+.Sh NAME
+.Nm pmap - hyra machine dependent virtual memory layer
+.Sh SYNOPSIS
+.In vm/pmap.h
+
+.Ft pmap_map(struct vm_ctx *, vaddr_t, paddr_t, vm_prot_t);
+.Sh DESCRIPTION
+The machine dependent virtual memory layer contains a standard set of
+functions that shall be implemented per architecture and left alone
+outside of vm(9). vm(9) uses pmap routines internally which allows for
+abstracting away machine dependent details.
+
+The
+.Ft pmap_map()
+function is used to map a physical address (paddr_t) to
+a virtual address (vaddr_t). The argument of type
+vm_prot_t is used to give a mapping certain access
+rules. These rules are described below:
+
+The
+.Ft PMAP_WRITABLE
+bit tells pmap_map() to allow writes to the page.
+Writes to pages without this bit will result in an exception,
+on AMD64 a #PF will occur.
+
+The
+.Ft PMAP_EXEC
+bit tells pmap_map() to allow this page to be
+executable. On platforms like AMD64, execution of pages
+without this bit will result in an exception from the
+instruction fetch, for AMD64, a #PF will occur.
+
+.Sh AUTHORS
+.An Ian Moffett Aq Mt ian@osmora.org
+
+.Sh SEE ALSO
+.Xr vm 9