ARM: P2V: introduce phys_to_virt/virt_to_phys runtime patching

This idea came from Nicolas, Eric Miao produced an initial version,
which was then rewritten into this.

Patch the physical to virtual translations at runtime.  As we modify
the code, this makes it incompatible with XIP kernels, but allows us
to achieve this with minimal loss of performance.

As many translations are of the form:

	physical = virtual + (PHYS_OFFSET - PAGE_OFFSET)
	virtual = physical - (PHYS_OFFSET - PAGE_OFFSET)

we generate an 'add' instruction for __virt_to_phys(), and a 'sub'
instruction for __phys_to_virt().  We calculate at run time (PHYS_OFFSET
- PAGE_OFFSET) by comparing the address prior to MMU initialization with
where it should be once the MMU has been initialized, and place this
constant into the above add/sub instructions.

Once we have (PHYS_OFFSET - PAGE_OFFSET), we can calculate the real
PHYS_OFFSET as PAGE_OFFSET is a build-time constant, and save this for
the C-mode PHYS_OFFSET variable definition to use.

At present, we are unable to support Realview with Sparsemem enabled
as this uses a complex mapping function, and MSM as this requires a
constant which will not fit in our math instruction.

Add a module version magic string for this feature to prevent
incompatible modules being loaded.

Tested-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Tested-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 56 insertions, 14 deletions

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index 2efec578a62e..7197879e1cb7 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -24,8 +24,6 @@
  */
 #define UL(x) _AC(x, UL)
 
-#define PHYS_OFFSET	PLAT_PHYS_OFFSET
-
 #ifdef CONFIG_MMU
 
 /*
@@ -135,16 +133,6 @@
 #endif
 
 /*
- * Physical vs virtual RAM address space conversion.  These are
- * private definitions which should NOT be used outside memory.h
- * files.  Use virt_to_phys/phys_to_virt/__pa/__va instead.
- */
-#ifndef __virt_to_phys
-#define __virt_to_phys(x)	((x) - PAGE_OFFSET + PHYS_OFFSET)
-#define __phys_to_virt(x)	((x) - PHYS_OFFSET + PAGE_OFFSET)
-#endif
-
-/*
  * Convert a physical address to a Page Frame Number and back
  */
 #define	__phys_to_pfn(paddr)	((paddr) >> PAGE_SHIFT)
@@ -159,6 +147,49 @@
 #ifndef __ASSEMBLY__
 
 /*
+ * Physical vs virtual RAM address space conversion.  These are
+ * private definitions which should NOT be used outside memory.h
+ * files.  Use virt_to_phys/phys_to_virt/__pa/__va instead.
+ */
+#ifndef __virt_to_phys
+#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
+
+extern unsigned long __pv_phys_offset;
+#define PHYS_OFFSET __pv_phys_offset
+
+#define __pv_stub(from,to,instr)			\
+	__asm__("@ __pv_stub\n"				\
+	"1:	" instr "	%0, %1, %2\n"		\
+	"	.pushsection .pv_table,\"a\"\n"		\
+	"	.long	1b\n"				\
+	"	.popsection\n"				\
+	: "=r" (to)					\
+	: "r" (from), "I" (0x81000000))
+
+static inline unsigned long __virt_to_phys(unsigned long x)
+{
+	unsigned long t;
+	__pv_stub(x, t, "add");
+	return t;
+}
+
+static inline unsigned long __phys_to_virt(unsigned long x)
+{
+	unsigned long t;
+	__pv_stub(x, t, "sub");
+	return t;
+}
+#else
+#define __virt_to_phys(x)	((x) - PAGE_OFFSET + PHYS_OFFSET)
+#define __phys_to_virt(x)	((x) - PHYS_OFFSET + PAGE_OFFSET)
+#endif
+#endif
+
+#ifndef PHYS_OFFSET
+#define PHYS_OFFSET	PLAT_PHYS_OFFSET
+#endif
+
+/*
  * The DMA mask corresponding to the maximum bus address allocatable
  * using GFP_DMA.  The default here places no restriction on DMA
  * allocations.  This must be the smallest DMA mask in the system,
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 12c8e680cbff..d072c21332ee 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -25,8 +25,19 @@ struct mod_arch_specific {
 };
 
 /*
- * Include the ARM architecture version.
+ * Add the ARM architecture version to the version magic string
  */
-#define MODULE_ARCH_VERMAGIC	"ARMv" __stringify(__LINUX_ARM_ARCH__) " "
+#define MODULE_ARCH_VERMAGIC_ARMVSN "ARMv" __stringify(__LINUX_ARM_ARCH__) " "
+
+/* Add __virt_to_phys patching state as well */
+#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
+#define MODULE_ARCH_VERMAGIC_P2V "p2v8 "
+#else
+#define MODULE_ARCH_VERMAGIC_P2V ""
+#endif
+
+#define MODULE_ARCH_VERMAGIC \
+	MODULE_ARCH_VERMAGIC_ARMVSN \
+	MODULE_ARCH_VERMAGIC_P2V
 
 #endif /* _ASM_ARM_MODULE_H */