arm64: 36 bit VA

36bit VA lets us use 2 level page tables while limiting the
available address space to 64GB.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Steve Capper <steve.capper@linaro.org>
Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

@@ -170,6 +170,7 @@ config FIX_EARLYCON_MEM
 
 config PGTABLE_LEVELS
 	int
+	default 2 if ARM64_16K_PAGES && ARM64_VA_BITS_36
 	default 2 if ARM64_64K_PAGES && ARM64_VA_BITS_42
 	default 3 if ARM64_64K_PAGES && ARM64_VA_BITS_48
 	default 3 if ARM64_4K_PAGES && ARM64_VA_BITS_39
@@ -391,6 +392,10 @@ choice
 	  space sizes. The level of translation table is determined by
 	  a combination of page size and virtual address space size.
 
+config ARM64_VA_BITS_36
+	bool "36-bit"
+	depends on ARM64_16K_PAGES
+
 config ARM64_VA_BITS_39
 	bool "39-bit"
 	depends on ARM64_4K_PAGES
@@ -410,6 +415,7 @@ endchoice
 
 config ARM64_VA_BITS
 	int
+	default 36 if ARM64_VA_BITS_36
 	default 39 if ARM64_VA_BITS_39
 	default 42 if ARM64_VA_BITS_42
 	default 47 if ARM64_VA_BITS_47
@@ -480,7 +486,7 @@ config ARCH_WANT_GENERAL_HUGETLB
 	def_bool y
 
 config ARCH_WANT_HUGE_PMD_SHARE
-	def_bool y if ARM64_4K_PAGES || ARM64_16K_PAGES
+	def_bool y if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
 
 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	def_bool y