[RFC 09/10] arm64/mm: Add FEAT_LPA2 specific fallback (48 bits PA) when not implemented

[Anshuman Khandual]

CONFIG_ARM64_PA_BITS_52 build kernels need to fallback for 48 bits PA range
encodings when FEAT_LPA2 is not implemented i.e TCR_EL1.DS could not be set
.  Hence modify applicable PTE and TTBR encoding helpers to accommodate the
scenario via 'arm64_lpa2_enabled'.

Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
 arch/arm64/include/asm/assembler.h     | 13 +++++++++++++
 arch/arm64/include/asm/pgtable-hwdef.h |  2 ++
 arch/arm64/include/asm/pgtable.h       | 12 ++++++++++--
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 0492543..844e9a0 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -615,6 +615,10 @@ alternative_endif
 	orr	\pte, \phys, \phys, lsr #36
 	and	\pte, \pte, #PTE_ADDR_MASK
 #elif defined(CONFIG_ARM64_PA_BITS_52_LPA2)
+	ldr_l   \tmp, arm64_lpa2_enabled
+	cmp     \tmp, #1
+	b.ne    .Lskip_lpa2\@
+
 	orr	\pte, \phys, \phys, lsr #42
 
 	/*
@@ -625,6 +629,9 @@ alternative_endif
 	mov	\tmp, #PTE_ADDR_LOW
 	orr	\tmp, \tmp, #PTE_ADDR_HIGH
 	and	\pte, \pte, \tmp
+
+.Lskip_lpa2\@:
+	mov	\pte, \phys
 #else  /* !CONFIG_ARM64_PA_BITS_52_LPA */
 	mov	\pte, \phys
 #endif /* CONFIG_ARM64_PA_BITS_52_LPA */
@@ -636,9 +643,15 @@ alternative_endif
 	bfxil	\phys, \pte, #PAGE_SHIFT, #(48 - PAGE_SHIFT)
 	lsl	\phys, \phys, #PAGE_SHIFT
 #elif defined(CONFIG_ARM64_PA_BITS_52_LPA2)
+	ldr_l   \phys, arm64_lpa2_enabled
+	cmp     \phys, #1
+	b.ne    .Lskip_lpa2\@
+
 	ubfiz	\phys, \pte, #(52 - PAGE_SHIFT - 10), #10
 	bfxil	\phys, \pte, #PAGE_SHIFT, #(50 - PAGE_SHIFT)
 	lsl	\phys, \phys, #PAGE_SHIFT
+.Lskip_lpa2\@:
+	and	\phys, \pte, #PTE_ADDR_MASK_48
 #else  /* !CONFIG_ARM64_PA_BITS_52_LPA */
 	and	\phys, \pte, #PTE_ADDR_MASK
 #endif /* CONFIG_ARM64_PA_BITS_52_LPA */
diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index 8a3b75e..b98b764 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -176,6 +176,8 @@
 #define PTE_ADDR_MASK		PTE_ADDR_LOW
 #endif /* CONFIG_ARM64_PA_BITS_52_LPA */
 
+#define PTE_ADDR_MASK_48	(((_AT(pteval_t, 1) << (48 - PAGE_SHIFT)) - 1) << PAGE_SHIFT)
+
 /*
  * AttrIndx[2:0] encoding (mapping attributes defined in the MAIR* registers).
  */
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 5e7e402..97b3cd2 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -71,9 +71,17 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 	((pte_val(pte) & PTE_ADDR_LOW) | ((pte_val(pte) & PTE_ADDR_HIGH) << 36))
 #define __phys_to_pte_val(phys)	(((phys) | ((phys) >> 36)) & PTE_ADDR_MASK)
 #elif defined(CONFIG_ARM64_PA_BITS_52_LPA2)
-#define __pte_to_phys(pte)	\
+#define __pte_to_phys_52(pte)	\
 	((pte_val(pte) & PTE_ADDR_LOW) | ((pte_val(pte) & PTE_ADDR_HIGH) << 42))
-#define __phys_to_pte_val(phys)	(((phys) | ((phys) >> 42)) & PTE_ADDR_MASK)
+#define __phys_to_pte_val_52(phys)	(((phys) | ((phys) >> 42)) & PTE_ADDR_MASK)
+
+#define __pte_to_phys_48(pte)		(pte_val(pte) & PTE_ADDR_MASK_48)
+#define __phys_to_pte_val_48(phys)	(phys)
+
+#define __pte_to_phys(pte)	\
+	(arm64_lpa2_enabled ? __pte_to_phys_52(pte) : __pte_to_phys_48(pte))
+#define __phys_to_pte_val(phys)	\
+	(arm64_lpa2_enabled ? __phys_to_pte_val_52(phys) : __phys_to_pte_val_48(phys))
 #else  /* !CONFIG_ARM64_PA_BITS_52_LPA */
 #define __pte_to_phys(pte)	(pte_val(pte) & PTE_ADDR_MASK)
 #define __phys_to_pte_val(phys)	(phys)
-- 
2.7.4