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arm64: mm: Introduce DEFAULT_MAP_WINDOW

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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>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Steve Capper
2018-12-06 22:50:37 +00:00
committed by Will Deacon
parent f6795053da
commit 363524d2b1
5 changed files with 12 additions and 6 deletions
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2
drivers/firmware/efi/libstub/arm-stub.c
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@@ -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