linux-stable/include/linux/highmem.h
Fabio M. De Francesco 85a85e7601 Documentation/vm: move "Using kmap-atomic" to highmem.h
The use of kmap_atomic() is new code is being deprecated in favor of
kmap_local_page().  For this reason the "Using kmap_atomic" section in
highmem.rst is obsolete and unnecessary, but it can still help developers
if it were moved to kdocs in highmem.h.

Therefore, move the relevant parts of this section from highmem.rst and
merge them with the kdocs in highmem.h.

Link: https://lkml.kernel.org/r/20220428212455.892-4-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-13 16:48:55 -07:00

431 lines
12 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_HIGHMEM_H
#define _LINUX_HIGHMEM_H
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/bug.h>
#include <linux/cacheflush.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/hardirq.h>
#include "highmem-internal.h"
/**
* kmap - Map a page for long term usage
* @page: Pointer to the page to be mapped
*
* Returns: The virtual address of the mapping
*
* Can only be invoked from preemptible task context because on 32bit
* systems with CONFIG_HIGHMEM enabled this function might sleep.
*
* For systems with CONFIG_HIGHMEM=n and for pages in the low memory area
* this returns the virtual address of the direct kernel mapping.
*
* The returned virtual address is globally visible and valid up to the
* point where it is unmapped via kunmap(). The pointer can be handed to
* other contexts.
*
* For highmem pages on 32bit systems this can be slow as the mapping space
* is limited and protected by a global lock. In case that there is no
* mapping slot available the function blocks until a slot is released via
* kunmap().
*/
static inline void *kmap(struct page *page);
/**
* kunmap - Unmap the virtual address mapped by kmap()
* @page: Pointer to the page which was mapped by kmap()
*
* Counterpart to kmap(). A NOOP for CONFIG_HIGHMEM=n and for mappings of
* pages in the low memory area.
*/
static inline void kunmap(struct page *page);
/**
* kmap_to_page - Get the page for a kmap'ed address
* @addr: The address to look up
*
* Returns: The page which is mapped to @addr.
*/
static inline struct page *kmap_to_page(void *addr);
/**
* kmap_flush_unused - Flush all unused kmap mappings in order to
* remove stray mappings
*/
static inline void kmap_flush_unused(void);
/**
* kmap_local_page - Map a page for temporary usage
* @page: Pointer to the page to be mapped
*
* Returns: The virtual address of the mapping
*
* Can be invoked from any context.
*
* Requires careful handling when nesting multiple mappings because the map
* management is stack based. The unmap has to be in the reverse order of
* the map operation:
*
* addr1 = kmap_local_page(page1);
* addr2 = kmap_local_page(page2);
* ...
* kunmap_local(addr2);
* kunmap_local(addr1);
*
* Unmapping addr1 before addr2 is invalid and causes malfunction.
*
* Contrary to kmap() mappings the mapping is only valid in the context of
* the caller and cannot be handed to other contexts.
*
* On CONFIG_HIGHMEM=n kernels and for low memory pages this returns the
* virtual address of the direct mapping. Only real highmem pages are
* temporarily mapped.
*
* While it is significantly faster than kmap() for the higmem case it
* comes with restrictions about the pointer validity. Only use when really
* necessary.
*
* On HIGHMEM enabled systems mapping a highmem page has the side effect of
* disabling migration in order to keep the virtual address stable across
* preemption. No caller of kmap_local_page() can rely on this side effect.
*/
static inline void *kmap_local_page(struct page *page);
/**
* kmap_local_folio - Map a page in this folio for temporary usage
* @folio: The folio containing the page.
* @offset: The byte offset within the folio which identifies the page.
*
* Requires careful handling when nesting multiple mappings because the map
* management is stack based. The unmap has to be in the reverse order of
* the map operation::
*
* addr1 = kmap_local_folio(folio1, offset1);
* addr2 = kmap_local_folio(folio2, offset2);
* ...
* kunmap_local(addr2);
* kunmap_local(addr1);
*
* Unmapping addr1 before addr2 is invalid and causes malfunction.
*
* Contrary to kmap() mappings the mapping is only valid in the context of
* the caller and cannot be handed to other contexts.
*
* On CONFIG_HIGHMEM=n kernels and for low memory pages this returns the
* virtual address of the direct mapping. Only real highmem pages are
* temporarily mapped.
*
* While it is significantly faster than kmap() for the higmem case it
* comes with restrictions about the pointer validity. Only use when really
* necessary.
*
* On HIGHMEM enabled systems mapping a highmem page has the side effect of
* disabling migration in order to keep the virtual address stable across
* preemption. No caller of kmap_local_folio() can rely on this side effect.
*
* Context: Can be invoked from any context.
* Return: The virtual address of @offset.
*/
static inline void *kmap_local_folio(struct folio *folio, size_t offset);
/**
* kmap_atomic - Atomically map a page for temporary usage - Deprecated!
* @page: Pointer to the page to be mapped
*
* Returns: The virtual address of the mapping
*
* In fact a wrapper around kmap_local_page() which also disables pagefaults
* and, depending on PREEMPT_RT configuration, also CPU migration and
* preemption. Therefore users should not count on the latter two side effects.
*
* Mappings should always be released by kunmap_atomic().
*
* Do not use in new code. Use kmap_local_page() instead.
*
* It is used in atomic context when code wants to access the contents of a
* page that might be allocated from high memory (see __GFP_HIGHMEM), for
* example a page in the pagecache. The API has two functions, and they
* can be used in a manner similar to the following:
*
* -- Find the page of interest. --
* struct page *page = find_get_page(mapping, offset);
*
* -- Gain access to the contents of that page. --
* void *vaddr = kmap_atomic(page);
*
* -- Do something to the contents of that page. --
* memset(vaddr, 0, PAGE_SIZE);
*
* -- Unmap that page. --
* kunmap_atomic(vaddr);
*
* Note that the kunmap_atomic() call takes the result of the kmap_atomic()
* call, not the argument.
*
* If you need to map two pages because you want to copy from one page to
* another you need to keep the kmap_atomic calls strictly nested, like:
*
* vaddr1 = kmap_atomic(page1);
* vaddr2 = kmap_atomic(page2);
*
* memcpy(vaddr1, vaddr2, PAGE_SIZE);
*
* kunmap_atomic(vaddr2);
* kunmap_atomic(vaddr1);
*/
static inline void *kmap_atomic(struct page *page);
/* Highmem related interfaces for management code */
static inline unsigned int nr_free_highpages(void);
static inline unsigned long totalhigh_pages(void);
#ifndef ARCH_HAS_FLUSH_ANON_PAGE
static inline void flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned long vmaddr)
{
}
#endif
#ifndef ARCH_IMPLEMENTS_FLUSH_KERNEL_VMAP_RANGE
static inline void flush_kernel_vmap_range(void *vaddr, int size)
{
}
static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
{
}
#endif
/* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */
#ifndef clear_user_highpage
static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
{
void *addr = kmap_local_page(page);
clear_user_page(addr, vaddr, page);
kunmap_local(addr);
}
#endif
#ifndef __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE_MOVABLE
/**
* alloc_zeroed_user_highpage_movable - Allocate a zeroed HIGHMEM page for a VMA that the caller knows can move
* @vma: The VMA the page is to be allocated for
* @vaddr: The virtual address the page will be inserted into
*
* Returns: The allocated and zeroed HIGHMEM page
*
* This function will allocate a page for a VMA that the caller knows will
* be able to migrate in the future using move_pages() or reclaimed
*
* An architecture may override this function by defining
* __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE_MOVABLE and providing their own
* implementation.
*/
static inline struct page *
alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
unsigned long vaddr)
{
struct page *page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
if (page)
clear_user_highpage(page, vaddr);
return page;
}
#endif
static inline void clear_highpage(struct page *page)
{
void *kaddr = kmap_local_page(page);
clear_page(kaddr);
kunmap_local(kaddr);
}
#ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
static inline void tag_clear_highpage(struct page *page)
{
}
#endif
/*
* If we pass in a base or tail page, we can zero up to PAGE_SIZE.
* If we pass in a head page, we can zero up to the size of the compound page.
*/
#ifdef CONFIG_HIGHMEM
void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
unsigned start2, unsigned end2);
#else
static inline void zero_user_segments(struct page *page,
unsigned start1, unsigned end1,
unsigned start2, unsigned end2)
{
void *kaddr = kmap_local_page(page);
unsigned int i;
BUG_ON(end1 > page_size(page) || end2 > page_size(page));
if (end1 > start1)
memset(kaddr + start1, 0, end1 - start1);
if (end2 > start2)
memset(kaddr + start2, 0, end2 - start2);
kunmap_local(kaddr);
for (i = 0; i < compound_nr(page); i++)
flush_dcache_page(page + i);
}
#endif
static inline void zero_user_segment(struct page *page,
unsigned start, unsigned end)
{
zero_user_segments(page, start, end, 0, 0);
}
static inline void zero_user(struct page *page,
unsigned start, unsigned size)
{
zero_user_segments(page, start, start + size, 0, 0);
}
#ifndef __HAVE_ARCH_COPY_USER_HIGHPAGE
static inline void copy_user_highpage(struct page *to, struct page *from,
unsigned long vaddr, struct vm_area_struct *vma)
{
char *vfrom, *vto;
vfrom = kmap_local_page(from);
vto = kmap_local_page(to);
copy_user_page(vto, vfrom, vaddr, to);
kunmap_local(vto);
kunmap_local(vfrom);
}
#endif
#ifndef __HAVE_ARCH_COPY_HIGHPAGE
static inline void copy_highpage(struct page *to, struct page *from)
{
char *vfrom, *vto;
vfrom = kmap_local_page(from);
vto = kmap_local_page(to);
copy_page(vto, vfrom);
kunmap_local(vto);
kunmap_local(vfrom);
}
#endif
static inline void memcpy_page(struct page *dst_page, size_t dst_off,
struct page *src_page, size_t src_off,
size_t len)
{
char *dst = kmap_local_page(dst_page);
char *src = kmap_local_page(src_page);
VM_BUG_ON(dst_off + len > PAGE_SIZE || src_off + len > PAGE_SIZE);
memcpy(dst + dst_off, src + src_off, len);
kunmap_local(src);
kunmap_local(dst);
}
static inline void memmove_page(struct page *dst_page, size_t dst_off,
struct page *src_page, size_t src_off,
size_t len)
{
char *dst = kmap_local_page(dst_page);
char *src = kmap_local_page(src_page);
VM_BUG_ON(dst_off + len > PAGE_SIZE || src_off + len > PAGE_SIZE);
memmove(dst + dst_off, src + src_off, len);
kunmap_local(src);
kunmap_local(dst);
}
static inline void memset_page(struct page *page, size_t offset, int val,
size_t len)
{
char *addr = kmap_local_page(page);
VM_BUG_ON(offset + len > PAGE_SIZE);
memset(addr + offset, val, len);
kunmap_local(addr);
}
static inline void memcpy_from_page(char *to, struct page *page,
size_t offset, size_t len)
{
char *from = kmap_local_page(page);
VM_BUG_ON(offset + len > PAGE_SIZE);
memcpy(to, from + offset, len);
kunmap_local(from);
}
static inline void memcpy_to_page(struct page *page, size_t offset,
const char *from, size_t len)
{
char *to = kmap_local_page(page);
VM_BUG_ON(offset + len > PAGE_SIZE);
memcpy(to + offset, from, len);
flush_dcache_page(page);
kunmap_local(to);
}
static inline void memzero_page(struct page *page, size_t offset, size_t len)
{
char *addr = kmap_local_page(page);
VM_BUG_ON(offset + len > PAGE_SIZE);
memset(addr + offset, 0, len);
flush_dcache_page(page);
kunmap_local(addr);
}
/**
* folio_zero_segments() - Zero two byte ranges in a folio.
* @folio: The folio to write to.
* @start1: The first byte to zero.
* @xend1: One more than the last byte in the first range.
* @start2: The first byte to zero in the second range.
* @xend2: One more than the last byte in the second range.
*/
static inline void folio_zero_segments(struct folio *folio,
size_t start1, size_t xend1, size_t start2, size_t xend2)
{
zero_user_segments(&folio->page, start1, xend1, start2, xend2);
}
/**
* folio_zero_segment() - Zero a byte range in a folio.
* @folio: The folio to write to.
* @start: The first byte to zero.
* @xend: One more than the last byte to zero.
*/
static inline void folio_zero_segment(struct folio *folio,
size_t start, size_t xend)
{
zero_user_segments(&folio->page, start, xend, 0, 0);
}
/**
* folio_zero_range() - Zero a byte range in a folio.
* @folio: The folio to write to.
* @start: The first byte to zero.
* @length: The number of bytes to zero.
*/
static inline void folio_zero_range(struct folio *folio,
size_t start, size_t length)
{
zero_user_segments(&folio->page, start, start + length, 0, 0);
}
#endif /* _LINUX_HIGHMEM_H */