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pmap_kextract(9): some additions

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Mainly, provide a little more detail on the caller's responsibilities.

Suggested by:	kib, jhb
Reviewed by:	kib, markj
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D42458
This commit is contained in:
Mitchell Horne 2023-11-06 12:54:18 -04:00
parent 8d6c0743e3
commit c1e2146821
1 changed files with 15 additions and 3 deletions
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18
share/man/man9/pmap_kextract.9
View file

@ -31,9 +31,21 @@ The
function retrieves the underlying physical memory address corresponding to the
given kernel virtual address
.Fa va .
The value of
The caller is responsible for ensuring that
.Fa va
must belong to a valid mapping in the kernel address space.
belongs to a valid mapping in the kernel address space.
The returned physical address is only meaningful as long as the mapping remains
stable, so the caller must also have some knowledge or guarantee of the
mapping's lifetime.
For example, it is invalid to call
.Fn pmap_kextract
with the address of a malloc'd object while there is a possibility for that
object to be freed concurrently.
.Pp
Unlike
.Xr pmap_extract 9 ,
.Fn pmap_kextract
is safe to be called from any context; it has no internal locking or sleep.
.Pp
.Fn vtophys
is an alias for
@ -42,7 +54,7 @@ and behaves identically.
.Sh RETURN VALUES
The
.Fn pmap_kextract
function returns the address of physical memory mapped at the kernel
function returns the physical address of memory mapped at the kernel
virtual address
.Fa va .
.Pp