arm64/mm: Simplify and document pte_to_phys() for 52 bit addresses

pte_to_phys() assembly definition does multiple bits field transformations
to derive physical address, embedded inside a page table entry. Unlike its
C counter part i.e __pte_to_phys(), pte_to_phys() is not very apparent. It
simplifies these operations via a new macro PTE_ADDR_HIGH_SHIFT indicating
how far the pte encoded higher address bits need to be left shifted. While
here, this also updates __pte_to_phys() and __phys_to_pte_val().

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20221107141753.2938621-1-anshuman.khandual@arm.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/assembler.h

@@ -660,12 +660,10 @@ alternative_endif
 	.endm
 
 	.macro	pte_to_phys, phys, pte
-#ifdef CONFIG_ARM64_PA_BITS_52
-	ubfiz	\phys, \pte, #(48 - 16 - 12), #16
-	bfxil	\phys, \pte, #16, #32
-	lsl	\phys, \phys, #16
-#else
 	and	\phys, \pte, #PTE_ADDR_MASK
+#ifdef CONFIG_ARM64_PA_BITS_52
+	orr	\phys, \phys, \phys, lsl #PTE_ADDR_HIGH_SHIFT
+	and	\phys, \phys, GENMASK_ULL(PHYS_MASK_SHIFT - 1, PAGE_SHIFT)
 #endif
 	.endm
 

arch/arm64/include/asm/pgtable-hwdef.h

@@ -159,6 +159,7 @@
 #ifdef CONFIG_ARM64_PA_BITS_52
 #define PTE_ADDR_HIGH		(_AT(pteval_t, 0xf) << 12)
 #define PTE_ADDR_MASK		(PTE_ADDR_LOW | PTE_ADDR_HIGH)
+#define PTE_ADDR_HIGH_SHIFT	36
 #else
 #define PTE_ADDR_MASK		PTE_ADDR_LOW
 #endif

arch/arm64/include/asm/pgtable.h

@@ -77,11 +77,11 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 static inline phys_addr_t __pte_to_phys(pte_t pte)
 {
 	return (pte_val(pte) & PTE_ADDR_LOW) |
-		((pte_val(pte) & PTE_ADDR_HIGH) << 36);
+		((pte_val(pte) & PTE_ADDR_HIGH) << PTE_ADDR_HIGH_SHIFT);
 }
 static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
 {
-	return (phys | (phys >> 36)) & PTE_ADDR_MASK;
+	return (phys | (phys >> PTE_ADDR_HIGH_SHIFT)) & PTE_ADDR_MASK;
 }
 #else
 #define __pte_to_phys(pte)	(pte_val(pte) & PTE_ADDR_MASK)