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