ARM: Add arm_memblock_steal() to allocate memory away from the kernel

Several platforms are now using the memblock_alloc+memblock_free+
memblock_remove trick to obtain memory which won't be mapped in the
kernel's page tables.  Most platforms do this (correctly) in the
->reserve callback.  However, OMAP has started to call these functions
outside of this callback, and this is extremely unsafe - memory will
not be unmapped, and could well be given out after memblock is no
longer responsible for its management.

So, provide arm_memblock_steal() to perform this function, and ensure
that it panic()s if it is used inappropriately.  Convert everyone
over, including OMAP.

As a result, OMAP with OMAP4_ERRATA_I688 enabled will panic on boot
with this change.  Mark this option as BROKEN and make it depend on
BROKEN.  OMAP needs to be fixed, or 137d105d50 (ARM: OMAP4: Fix
errata i688 with MPU interconnect barriers.) reverted until such
time it can be fixed correctly.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 17 insertions, 0 deletions

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index e34ea8adc1f9..6ec1226fc62d 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -22,6 +22,7 @@
 #include <linux/memblock.h>
 
 #include <asm/mach-types.h>
+#include <asm/memblock.h>
 #include <asm/prom.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
@@ -307,6 +308,21 @@ static void arm_memory_present(void)
 }
 #endif
 
+static bool arm_memblock_steal_permitted = true;
+
+phys_addr_t arm_memblock_steal(phys_addr_t size, phys_addr_t align)
+{
+        phys_addr_t phys;
+
+        BUG_ON(!arm_memblock_steal_permitted);
+
+        phys = memblock_alloc(size, align);
+        memblock_free(phys, size);
+        memblock_remove(phys, size);
+
+        return phys;
+}
+
 void __init arm_memblock_init(struct meminfo *mi, struct machine_desc *mdesc)
 {
         int i;
@@ -349,6 +365,7 @@ void __init arm_memblock_init(struct meminfo *mi, struct machine_desc *mdesc)
         if (mdesc->reserve)
                 mdesc->reserve();
 
+        arm_memblock_steal_permitted = false;
         memblock_allow_resize();
         memblock_dump_all();
 }