focal (9) pmap_quick_enter_page.9freebsd.gz

Provided by: freebsd-manpages_12.0-1_all bug

NAME
     pmap_quick_enter_page, pmap_quick_remove_page — manage fast, single-page kernel address space mappings


SYNOPSIS
     #include <sys/param.h>
     #include <vm/vm.h>
     #include <vm/pmap.h>

     vm_offset_t
     pmap_quick_enter_page(vm_page_t m);

     void
     pmap_quick_remove_page(vm_offset_t kva);


DESCRIPTION
     The pmap_quick_enter_page() function accepts a single page 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.

     The pmap_quick_remove_page() function removes a mapping previously created by pmap_quick_enter_page() at
     kva, making the KVA frame used by pmap_quick_enter_page() available for reuse.

     On many architectures, pmap_quick_enter_page() uses a per-CPU pageframe.  In those cases, it must disable
     preemption on the local CPU.  The corresponding call to 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 pmap_quick_enter_page() must not be nested.

     pmap_quick_enter_page() and pmap_quick_remove_page() do not sleep, and 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.

     The page 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.


RETURN VALUES
     The pmap_quick_enter_page() function returns the kernel virtual address that is mapped to the page m.


SEE ALSO
     pmap(9)


AUTHORS
     This manual page was written by Jason A Harmening <jah@FreeBSD.org>.