Sometimes we have memories that are supposed to be read-only, but when
we map these regions the best we can do is map them as write-back with
MEMREMAP_WB. Introduce a read-only memory mapping (MEMREMAP_RO) that
allows us to map reserved memory regions as read-only. This way, we're
less likely to see these special memory regions become corrupted by
stray writes to them.
Cc: Evan Green <evgreen@xxxxxxxxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Cc: Andy Gross <agross@xxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
---
include/linux/io.h | 1 +
kernel/iomem.c | 20 +++++++++++++++++---
2 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/include/linux/io.h b/include/linux/io.h
index accac822336a..15a63efcd153 100644
--- a/include/linux/io.h
+++ b/include/linux/io.h
@@ -148,6 +148,7 @@ enum {
MEMREMAP_WC = 1 << 2,
MEMREMAP_ENC = 1 << 3,
MEMREMAP_DEC = 1 << 4,
+ MEMREMAP_RO = 1 << 5,
};
void *memremap(resource_size_t offset, size_t size, unsigned long flags);
diff --git a/kernel/iomem.c b/kernel/iomem.c
index 62c92e43aa0d..6d76b7398714 100644
--- a/kernel/iomem.c
+++ b/kernel/iomem.c
@@ -19,6 +19,13 @@ static void *arch_memremap_wb(resource_size_t offset, unsigned long size)
}
#endif
+#ifndef arch_memremap_ro
+static void *arch_memremap_ro(resource_size_t offset, unsigned long size)
+{
+ return NULL;
+}
+#endif
+
#ifndef arch_memremap_can_ram_remap
static bool arch_memremap_can_ram_remap(resource_size_t offset, size_t size,
unsigned long flags)
@@ -45,7 +52,7 @@ static void *try_ram_remap(resource_size_t offset, size_t size,
* @offset: iomem resource start address
* @size: size of remap
* @flags: any of MEMREMAP_WB, MEMREMAP_WT, MEMREMAP_WC,
- * MEMREMAP_ENC, MEMREMAP_DEC
+ * MEMREMAP_ENC, MEMREMAP_DEC, MEMREMAP_RO
*
* memremap() is "ioremap" for cases where it is known that the resource
* being mapped does not have i/o side effects and the __iomem
@@ -53,6 +60,9 @@ static void *try_ram_remap(resource_size_t offset, size_t size,
* mapping types will be attempted in the order listed below until one of
* them succeeds.
*
+ * MEMREMAP_RO - establish a mapping whereby writes are ignored/rejected.
+ * Attempts to map System RAM with this mapping type will fail.
+ *
* MEMREMAP_WB - matches the default mapping for System RAM on
* the architecture. This is usually a read-allocate write-back cache.
* Moreover, if MEMREMAP_WB is specified and the requested remap region is RAM
@@ -84,7 +94,10 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
}
/* Try all mapping types requested until one returns non-NULL */
- if (flags & MEMREMAP_WB) {
+ if ((flags & MEMREMAP_RO) && is_ram != REGION_INTERSECTS)
+ addr = arch_memremap_ro(offset, size);
+
+ if (!addr && (flags & MEMREMAP_WB)) {
/*
* MEMREMAP_WB is special in that it can be satisfied
* from the direct map. Some archs depend on the
@@ -103,7 +116,8 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
* address mapping. Enforce that this mapping is not aliasing
* System RAM.
*/
- if (!addr && is_ram == REGION_INTERSECTS && flags != MEMREMAP_WB) {
+ if (!addr && is_ram == REGION_INTERSECTS &&
+ (flags != MEMREMAP_WB || flags != MEMREMAP_RO)) {
WARN_ONCE(1, "memremap attempted on ram %pa size: %#lx\n",
&offset, (unsigned long) size);
return NULL;
--
Sent by a computer through tubes
