Commit 92281dee authored by Dan Williams's avatar Dan Williams
Browse files

arch: introduce memremap()

Existing users of ioremap_cache() are mapping memory that is known in
advance to not have i/o side effects.  These users are forced to cast
away the __iomem annotation, or otherwise neglect to fix the sparse
errors thrown when dereferencing pointers to this memory.  Provide
memremap() as a non __iomem annotated ioremap_*() in the case when
ioremap is otherwise a pointer to cacheable memory. Empirically,
ioremap_<cacheable-type>() call sites are seeking memory-like semantics
(e.g.  speculative reads, and prefetching permitted).

memremap() is a break from the ioremap implementation pattern of adding
a new memremap_<type>() for each mapping type and having silent
compatibility fall backs.  Instead, the implementation defines flags
that are passed to the central memremap() and if a mapping type is not
supported by an arch memremap returns NULL.

We introduce a memremap prototype as a trivial wrapper of
ioremap_cache() and ioremap_wt().  Later, once all ioremap_cache() and
ioremap_wt() usage has been removed from drivers we teach archs to
implement arch_memremap() with the ability to strictly enforce the
mapping type.

Cc: Arnd Bergmann <>
Reviewed-by: default avatarChristoph Hellwig <>
Signed-off-by: default avatarDan Williams <>
parent 92b19ff5
......@@ -435,6 +435,7 @@ static inline void __iomem * ioremap_cache (unsigned long phys_addr, unsigned lo
return ioremap(phys_addr, size);
#define ioremap_cache ioremap_cache
......@@ -342,6 +342,7 @@ ioremap_cache(phys_addr_t offset, unsigned long size)
return __ioremap_mode(offset, size, PAGE_KERNEL);
#define ioremap_cache ioremap_cache
static inline void __iomem *
......@@ -57,6 +57,7 @@ static inline void __iomem *ioremap_cache(unsigned long offset,
#define ioremap_cache ioremap_cache
#define ioremap_wc ioremap_nocache
#define ioremap_wt ioremap_nocache
......@@ -121,4 +121,13 @@ static inline int arch_phys_wc_index(int handle)
enum {
/* See memremap() kernel-doc for usage description... */
MEMREMAP_WB = 1 << 0,
MEMREMAP_WT = 1 << 1,
void *memremap(resource_size_t offset, size_t size, unsigned long flags);
void memunmap(void *addr);
#endif /* _LINUX_IO_H */
......@@ -99,6 +99,8 @@ obj-$(CONFIG_JUMP_LABEL) += jump_label.o
obj-$(CONFIG_CONTEXT_TRACKING) += context_tracking.o
obj-$(CONFIG_TORTURE_TEST) += torture.o
obj-$(CONFIG_HAS_IOMEM) += memremap.o
$(obj)/configs.o: $(obj)/config_data.h
# config_data.h contains the same information as ikconfig.h but gzipped.
* Copyright(c) 2015 Intel Corporation. All rights reserved.
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* General Public License for more details.
#include <linux/types.h>
#include <linux/io.h>
#include <linux/mm.h>
#ifndef ioremap_cache
/* temporary while we convert existing ioremap_cache users to memremap */
__weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size)
return ioremap(offset, size);
* memremap() - remap an iomem_resource as cacheable memory
* @offset: iomem resource start address
* @size: size of remap
* @flags: either MEMREMAP_WB or MEMREMAP_WT
* memremap() is "ioremap" for cases where it is known that the resource
* being mapped does not have i/o side effects and the __iomem
* annotation is not applicable.
* MEMREMAP_WB - matches the default mapping for "System RAM" on
* the architecture. This is usually a read-allocate write-back cache.
* Morever, if MEMREMAP_WB is specified and the requested remap region is RAM
* memremap() will bypass establishing a new mapping and instead return
* a pointer into the direct map.
* MEMREMAP_WT - establish a mapping whereby writes either bypass the
* cache or are written through to memory and never exist in a
* cache-dirty state with respect to program visibility. Attempts to
* map "System RAM" with this mapping type will fail.
void *memremap(resource_size_t offset, size_t size, unsigned long flags)
int is_ram = region_intersects(offset, size, "System RAM");
void *addr = NULL;
if (is_ram == REGION_MIXED) {
WARN_ONCE(1, "memremap attempted on mixed range %pa size: %#lx\n",
&offset, (unsigned long) size);
return NULL;
/* Try all mapping types requested until one returns non-NULL */
if (flags & MEMREMAP_WB) {
flags &= ~MEMREMAP_WB;
* MEMREMAP_WB is special in that it can be satisifed
* from the direct map. Some archs depend on the
* capability of memremap() to autodetect cases where
* the requested range is potentially in "System RAM"
if (is_ram == REGION_INTERSECTS)
addr = __va(offset);
addr = ioremap_cache(offset, size);
* If we don't have a mapping yet and more request flags are
* pending then we will be attempting to establish a new virtual
* address mapping. Enforce that this mapping is not aliasing
* "System RAM"
if (!addr && is_ram == REGION_INTERSECTS && flags) {
WARN_ONCE(1, "memremap attempted on ram %pa size: %#lx\n",
&offset, (unsigned long) size);
return NULL;
if (!addr && (flags & MEMREMAP_WT)) {
flags &= ~MEMREMAP_WT;
addr = ioremap_wt(offset, size);
return addr;
void memunmap(void *addr)
if (is_vmalloc_addr(addr))
iounmap((void __iomem *) addr);
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment