ARM: mm: Correct virt_to_phys patching for 64 bit physical addresses

The current phys_to_virt patching mechanism works only for 32 bit
physical addresses and this patch extends the idea for 64bit physical
addresses.

The 64bit v2p patching mechanism patches the higher 8 bits of physical
address with a constant using 'mov' instruction and lower 32bits are patched
using 'add'. While this is correct, in those platforms where the lowmem addressable
physical memory spawns across 4GB boundary, a carry bit can be produced as a
result of addition of lower 32bits. This has to be taken in to account and added
in to the upper. The patched __pv_offset and va are added in lower 32bits, where
__pv_offset can be in two's complement form when PA_START < VA_START and that can
result in a false carry bit.

e.g
    1) PA = 0x80000000; VA = 0xC0000000
       __pv_offset = PA - VA = 0xC0000000 (2's complement)

    2) PA = 0x2 80000000; VA = 0xC000000
       __pv_offset = PA - VA = 0x1 C0000000

So adding __pv_offset + VA should never result in a true overflow for (1).
So in order to differentiate between a true carry, a __pv_offset is extended
to 64bit and the upper 32bits will have 0xffffffff if __pv_offset is
2's complement. So 'mvn #0' is inserted instead of 'mov' while patching
for the same reason. Since mov, add, sub instruction are to patched
with different constants inside the same stub, the rotation field
of the opcode is using to differentiate between them.

So the above examples for v2p translation becomes for VA=0xC0000000,
    1) PA[63:32] = 0xffffffff
       PA[31:0] = VA + 0xC0000000 --> results in a carry
       PA[63:32] = PA[63:32] + carry

       PA[63:0] = 0x0 80000000

    2) PA[63:32] = 0x1
       PA[31:0] = VA + 0xC0000000 --> results in a carry
       PA[63:32] = PA[63:32] + carry

       PA[63:0] = 0x2 80000000

The above ideas were suggested by Nicolas Pitre <nico@linaro.org> as
part of the review of first and second versions of the subject patch.

There is no corresponding change on the phys_to_virt() side, because
computations on the upper 32-bits would be discarded anyway.

Cc: Russell King <linux@arm.linux.org.uk>

Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Sricharan R <r.sricharan@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

1 files changed, 34 insertions, 3 deletions

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index d9b96c65e594..6748d6295a1a 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -172,9 +172,14 @@
  * so that all we need to do is modify the 8-bit constant field.
  */
 #define __PV_BITS_31_24	0x81000000
+#define __PV_BITS_7_0	0x81
 
 extern phys_addr_t (*arch_virt_to_idmap) (unsigned long x);
-extern unsigned long __pv_phys_offset;
+extern u64 __pv_phys_offset;
+extern u64 __pv_offset;
+extern void fixup_pv_table(const void *, unsigned long);
+extern const void *__pv_table_begin, *__pv_table_end;
+
 #define PHYS_OFFSET __pv_phys_offset
 
 #define __pv_stub(from,to,instr,type)			\
@@ -186,10 +191,36 @@ extern unsigned long __pv_phys_offset;
 	: "=r" (to)					\
 	: "r" (from), "I" (type))
 
+#define __pv_stub_mov_hi(t)				\
+	__asm__ volatile("@ __pv_stub_mov\n"		\
+	"1:	mov	%R0, %1\n"			\
+	"	.pushsection .pv_table,\"a\"\n"		\
+	"	.long	1b\n"				\
+	"	.popsection\n"				\
+	: "=r" (t)					\
+	: "I" (__PV_BITS_7_0))
+
+#define __pv_add_carry_stub(x, y)			\
+	__asm__ volatile("@ __pv_add_carry_stub\n"	\
+	"1:	adds	%Q0, %1, %2\n"			\
+	"	adc	%R0, %R0, #0\n"			\
+	"	.pushsection .pv_table,\"a\"\n"		\
+	"	.long	1b\n"				\
+	"	.popsection\n"				\
+	: "+r" (y)					\
+	: "r" (x), "I" (__PV_BITS_31_24)		\
+	: "cc")
+
 static inline phys_addr_t __virt_to_phys(unsigned long x)
 {
-	unsigned long t;
-	__pv_stub(x, t, "add", __PV_BITS_31_24);
+	phys_addr_t t;
+
+	if (sizeof(phys_addr_t) == 4) {
+		__pv_stub(x, t, "add", __PV_BITS_31_24);
+	} else {
+		__pv_stub_mov_hi(t);
+		__pv_add_carry_stub(x, t);
+	}
 	return t;
 }