[PATCH] arm64/mm: Describe 52 bits PA folding into TTBRx_EL1

[Anshuman Khandual <anshuman.khandual@arm.com>]

A 52 bits physical address gets stored in TTBR_BADDR_MASK_52 in a folded
manner. Shifting PA[51:0] right ward by '46' bits, aligns PA[51:48] into
TTBRx_EL1[5:2] which gets ORed for the final TTBRx_EL1 encoding.

Define TTBR_BADDR_HIGH_52_PA_PIVOT which describes this inflection point,
where this right shift is done thus bringing some clarity to this 52 bits
PA address folding process in TTBRx_EL1.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
This applies on v7.0-rc1

Earlier context can be found here.

https://lore.kernel.org/linux-arm-kernel/aRb8ezhQd0c0jp9G@J2N7QTR9R3/

 arch/arm64/include/asm/assembler.h     |  2 +-
 arch/arm64/include/asm/pgtable-hwdef.h | 14 ++++++++++++++
 arch/arm64/include/asm/pgtable.h       |  3 ++-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index d3d46e5f7188..a68002dd4c0e 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -615,7 +615,7 @@ alternative_else_nop_endif
  */
 	.macro	phys_to_ttbr, ttbr, phys
 #ifdef CONFIG_ARM64_PA_BITS_52
-	orr	\ttbr, \phys, \phys, lsr #46
+	orr	\ttbr, \phys, \phys, lsr #TTBR_BADDR_52_PA_PIVOT
 	and	\ttbr, \ttbr, #TTBR_BADDR_MASK_52
 #else
 	mov	\ttbr, \phys
diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index d49180bb7cb3..21ca79f02a5d 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -284,6 +284,20 @@
  * TTBR_ELx[1] is RES0 in this configuration.
  */
 #define TTBR_BADDR_MASK_52	GENMASK_ULL(47, 2)
+
+/*
+ * A 52 bit physical address gets stored in TTBR_BADDR_MASK_52 i.e
+ * GENMASK(47, 2) in a folded manner. Shifting PA[51:0] right ward
+ * by 46 bits aligns PA[51:48] into TTBRx_EL1[5:2] which gets ORed
+ * subsequently for the final TTBRx_EL1 encoding.
+ *
+ * 47                                              5          2  0
+ * +----------------------------------------------+-----------+--+
+ * |                      PA[47:X]                | PA[51:48] |  |
+ * +----------------------------------------------+-----------+--+
+ *
+ */
+#define TTBR_BADDR_52_PA_PIVOT (51 - 5)
 #endif
 
 #ifdef CONFIG_ARM64_VA_BITS_52
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b3e58735c49b..2f274c468d83 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1576,7 +1576,8 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
 #define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)
 
 #ifdef CONFIG_ARM64_PA_BITS_52
-#define phys_to_ttbr(addr)	(((addr) | ((addr) >> 46)) & TTBR_BADDR_MASK_52)
+#define phys_to_ttbr(addr)	(((addr) | ((addr) >> TTBR_BADDR_52_PA_PIVOT)) & \
+				 TTBR_BADDR_MASK_52)
 #else
 #define phys_to_ttbr(addr)	(addr)
 #endif
-- 
2.30.2