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arm64: Support ARM64_VA_BITS=52 when setting ARCH_MMAP_RND_BITS_MAX

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[ Upstream commit f101c56447717c595d803894ba0e215f56c6fba4 ]

When the 52-bit virtual addressing was introduced the select like
ARCH_MMAP_RND_BITS_MAX logic was never updated to account for it.
Because of that the rnd max bits knob is set to the default value of 18
when ARM64_VA_BITS=52.
Fix this by setting ARCH_MMAP_RND_BITS_MAX to the same value that would
be used if 48-bit addressing was used. Higher values can't used here
because 52-bit addressing is used only if the caller provides a hint to
mmap, with a fallback to 48-bit. The knob in question is an upper bound
for what the user can set in /proc/sys/vm/mmap_rnd_bits, which in turn
is used to determine how many random bits can be inserted into the base
address used for mmap allocations. Since 48-bit allocations are legal
with ARM64_VA_BITS=52, we need to make sure that the base address is
small enough to facilitate this.

Fixes: b6d00d47e8 ("arm64: mm: Introduce 52-bit Kernel VAs")
Signed-off-by: Kornel Dulęba <korneld@google.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20250417114754.3238273-1-korneld@google.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Kornel Dulęba 2025-04-17 11:47:54 +00:00 committed by Greg Kroah-Hartman
parent 0052f10c25
commit cf08a1cba0
1 changed files with 3 additions and 3 deletions
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6
arch/arm64/Kconfig
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@ -304,9 +304,9 @@ config ARCH_MMAP_RND_BITS_MAX
default 24 if ARM64_VA_BITS=39
default 27 if ARM64_VA_BITS=42
default 30 if ARM64_VA_BITS=47
default 29 if ARM64_VA_BITS=48 && ARM64_64K_PAGES
default 31 if ARM64_VA_BITS=48 && ARM64_16K_PAGES
default 33 if ARM64_VA_BITS=48
default 29 if (ARM64_VA_BITS=48 || ARM64_VA_BITS=52) && ARM64_64K_PAGES
default 31 if (ARM64_VA_BITS=48 || ARM64_VA_BITS=52) && ARM64_16K_PAGES
default 33 if (ARM64_VA_BITS=48 || ARM64_VA_BITS=52)
default 14 if ARM64_64K_PAGES
default 16 if ARM64_16K_PAGES
default 18