[PATCH V3 2/5] arm64: mm: Introduce DEFAULT_MAP_WINDOW

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

We wish to introduce a 52-bit virtual address space for userspace but
maintain compatibility with software that assumes the maximum VA space
size is 48 bit.

In order to achieve this, on 52-bit VA systems, we make mmap behave as
if it were running on a 48-bit VA system (unless userspace explicitly
requests a VA where addr[51:48] != 0).

On a system running a 52-bit userspace we need TASK_SIZE to represent
the 52-bit limit as it is used in various places to distinguish between
kernelspace and userspace addresses.

Thus we need a new limit for mmap, stack, ELF loader and EFI (which uses
TTBR0) to represent the non-extended VA space.

This patch introduces DEFAULT_MAP_WINDOW and DEFAULT_MAP_WINDOW_64 and
switches the appropriate logic to use that instead of TASK_SIZE.

Signed-off-by: Steve Capper <steve.capper@arm.com>

---

Changed in V3: corrections to allow COMPAT 32-bit EL0 mode to work
---
 arch/arm64/include/asm/elf.h            |  2 +-
 arch/arm64/include/asm/processor.h      | 10 ++++++++--
 arch/arm64/mm/init.c                    |  2 +-
 drivers/firmware/efi/arm-runtime.c      |  2 +-
 drivers/firmware/efi/libstub/arm-stub.c |  2 +-
 5 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 433b9554c6a1..bc9bd9e77d9d 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -117,7 +117,7 @@
  * 64-bit, this is above 4GB to leave the entire 32-bit address
  * space open for things that want to use the area for 32-bit pointers.
  */
-#define ELF_ET_DYN_BASE		(2 * TASK_SIZE_64 / 3)
+#define ELF_ET_DYN_BASE		(2 * DEFAULT_MAP_WINDOW_64 / 3)
 
 #ifndef __ASSEMBLY__
 
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 3e2091708b8e..da41a2655b69 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -25,6 +25,9 @@
 #define USER_DS		(TASK_SIZE_64 - 1)
 
 #ifndef __ASSEMBLY__
+
+#define DEFAULT_MAP_WINDOW_64	(UL(1) << VA_BITS)
+
 #ifdef __KERNEL__
 
 #include <linux/build_bug.h>
@@ -51,13 +54,16 @@
 				TASK_SIZE_32 : TASK_SIZE_64)
 #define TASK_SIZE_OF(tsk)	(test_tsk_thread_flag(tsk, TIF_32BIT) ? \
 				TASK_SIZE_32 : TASK_SIZE_64)
+#define DEFAULT_MAP_WINDOW	(test_thread_flag(TIF_32BIT) ? \
+				TASK_SIZE_32 : DEFAULT_MAP_WINDOW_64)
 #else
 #define TASK_SIZE		TASK_SIZE_64
+#define DEFAULT_MAP_WINDOW	DEFAULT_MAP_WINDOW_64
 #endif /* CONFIG_COMPAT */
 
-#define TASK_UNMAPPED_BASE	(PAGE_ALIGN(TASK_SIZE / 4))
+#define TASK_UNMAPPED_BASE	(PAGE_ALIGN(DEFAULT_MAP_WINDOW / 4))
+#define STACK_TOP_MAX		DEFAULT_MAP_WINDOW_64
 
-#define STACK_TOP_MAX		TASK_SIZE_64
 #ifdef CONFIG_COMPAT
 #define AARCH32_VECTORS_BASE	0xffff0000
 #define STACK_TOP		(test_thread_flag(TIF_32BIT) ? \
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 9d9582cac6c4..e5a1dc0beef9 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -609,7 +609,7 @@ void __init mem_init(void)
 	 * detected at build time already.
 	 */
 #ifdef CONFIG_COMPAT
-	BUILD_BUG_ON(TASK_SIZE_32			> TASK_SIZE_64);
+	BUILD_BUG_ON(TASK_SIZE_32			> DEFAULT_MAP_WINDOW_64);
 #endif
 
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
diff --git a/drivers/firmware/efi/arm-runtime.c b/drivers/firmware/efi/arm-runtime.c
index 922cfb813109..952cec5b611a 100644
--- a/drivers/firmware/efi/arm-runtime.c
+++ b/drivers/firmware/efi/arm-runtime.c
@@ -38,7 +38,7 @@ static struct ptdump_info efi_ptdump_info = {
 	.mm		= &efi_mm,
 	.markers	= (struct addr_marker[]){
 		{ 0,		"UEFI runtime start" },
-		{ TASK_SIZE_64,	"UEFI runtime end" }
+		{ DEFAULT_MAP_WINDOW_64, "UEFI runtime end" }
 	},
 	.base_addr	= 0,
 };
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 30ac0c975f8a..d1ec7136e3e1 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -33,7 +33,7 @@
 #define EFI_RT_VIRTUAL_SIZE	SZ_512M
 
 #ifdef CONFIG_ARM64
-# define EFI_RT_VIRTUAL_LIMIT	TASK_SIZE_64
+# define EFI_RT_VIRTUAL_LIMIT	DEFAULT_MAP_WINDOW_64
 #else
 # define EFI_RT_VIRTUAL_LIMIT	TASK_SIZE
 #endif
-- 
2.11.0