[PATCH V4 05/11] arm64: mm: Introduce VA_BITS_MIN

[Steve Capper <steve.capper@arm.com>]

In order to support 52-bit kernel addresses detectable at boot time, the
kernel needs to know the most conservative VA_BITS possible should it
need to fall back to this quantity due to lack of hardware support.

A new compile time constant VA_BITS_MIN is introduced in this patch and
it is employed in the KASAN end address, KASLR, and EFI stub.

For Arm, if 52-bit VA support is unavailable the fallback is to 48-bits.

In other words: VA_BITS_MIN = min (48, VA_BITS)

Signed-off-by: Steve Capper <steve.capper@arm.com>
---
 arch/arm64/Kconfig                 | 4 ++++
 arch/arm64/include/asm/efi.h       | 4 ++--
 arch/arm64/include/asm/memory.h    | 5 ++++-
 arch/arm64/include/asm/processor.h | 2 +-
 arch/arm64/kernel/head.S           | 2 +-
 arch/arm64/kernel/kaslr.c          | 6 +++---
 arch/arm64/mm/kasan_init.c         | 3 ++-
 7 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f7f23e47c28f..0206804b0868 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -797,6 +797,10 @@ config ARM64_VA_BITS
 	default 47 if ARM64_VA_BITS_47
 	default 48 if ARM64_VA_BITS_48 || ARM64_USER_VA_BITS_52
 
+config ARM64_VA_BITS_MIN
+	int
+	default ARM64_VA_BITS
+
 choice
 	prompt "Physical address space size"
 	default ARM64_PA_BITS_48
diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index 8e79ce9c3f5c..f6dbc0149dae 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -79,7 +79,7 @@ static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
 
 /*
  * On arm64, we have to ensure that the initrd ends up in the linear region,
- * which is a 1 GB aligned region of size '1UL << (VA_BITS - 1)' that is
+ * which is a 1 GB aligned region of size '1UL << (VA_BITS_MIN - 1)' that is
  * guaranteed to cover the kernel Image.
  *
  * Since the EFI stub is part of the kernel Image, we can relax the
@@ -90,7 +90,7 @@ static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
 static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
 						    unsigned long image_addr)
 {
-	return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS - 1));
+	return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS_MIN - 1));
 }
 
 #define efi_call_early(f, ...)		sys_table_arg->boottime->f(__VA_ARGS__)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 8b0f1599b2d1..a8a91a573bff 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -52,6 +52,9 @@
 #define PCI_IO_END		(VMEMMAP_START - SZ_2M)
 #define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)
 #define FIXADDR_TOP		(PCI_IO_START - SZ_2M)
+#define VA_BITS_MIN		(CONFIG_ARM64_VA_BITS_MIN)
+#define _VA_START(va)		(UL(0xffffffffffffffff) - \
+				(UL(1) << ((va) - 1)) + 1)
 
 #define KERNEL_START      _text
 #define KERNEL_END        _end
@@ -78,7 +81,7 @@
 #endif
 #else
 #define KASAN_THREAD_SHIFT	0
-#define KASAN_SHADOW_END	(VA_START)
+#define KASAN_SHADOW_END	(_VA_START(VA_BITS_MIN))
 #endif
 
 #define MIN_THREAD_SHIFT	(14 + KASAN_THREAD_SHIFT)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 844e2964b0f5..0e1f2770192a 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -42,7 +42,7 @@
  * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area.
  */
 
-#define DEFAULT_MAP_WINDOW_64	(UL(1) << VA_BITS)
+#define DEFAULT_MAP_WINDOW_64	(UL(1) << VA_BITS_MIN)
 #define TASK_SIZE_64		(UL(1) << vabits_user)
 
 #ifdef CONFIG_COMPAT
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 2cdacd1c141b..ac58c69993ec 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -314,7 +314,7 @@ __create_page_tables:
 	mov	x5, #52
 	cbnz	x6, 1f
 #endif
-	mov	x5, #VA_BITS
+	mov	x5, #VA_BITS_MIN
 1:
 	adr_l	x6, vabits_user
 	str	x5, [x6]
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 708051655ad9..5a59f7567f9c 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -116,15 +116,15 @@ u64 __init kaslr_early_init(u64 dt_phys)
 	/*
 	 * OK, so we are proceeding with KASLR enabled. Calculate a suitable
 	 * kernel image offset from the seed. Let's place the kernel in the
-	 * middle half of the VMALLOC area (VA_BITS - 2), and stay clear of
+	 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
 	 * the lower and upper quarters to avoid colliding with other
 	 * allocations.
 	 * Even if we could randomize at page granularity for 16k and 64k pages,
 	 * let's always round to 2 MB so we don't interfere with the ability to
 	 * map using contiguous PTEs
 	 */
-	mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1);
-	offset = BIT(VA_BITS - 3) + (seed & mask);
+	mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1);
+	offset = BIT(VA_BITS_MIN - 3) + (seed & mask);
 
 	/* use the top 16 bits to randomize the linear region */
 	memstart_offset_seed = seed >> 48;
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 9e68e3d12956..881d545d252a 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -154,7 +154,8 @@ static void __init kasan_pgd_populate(unsigned long addr, unsigned long end,
 /* The early shadow maps everything to a single page of zeroes */
 asmlinkage void __init kasan_early_init(void)
 {
-	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_START, PGDIR_SIZE));
+	BUILD_BUG_ON(!IS_ALIGNED(_KASAN_SHADOW_START(VA_BITS), PGDIR_SIZE));
+	BUILD_BUG_ON(!IS_ALIGNED(_KASAN_SHADOW_START(VA_BITS_MIN), PGDIR_SIZE));
 	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));
 	kasan_pgd_populate(KASAN_SHADOW_START, KASAN_SHADOW_END, NUMA_NO_NODE,
 			   true);
-- 
2.20.1


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