[PATCH v2] arm64: Support ARM64_VA_BITS=52 when setting ARCH_MMAP_RND_BITS_MAX

[Will Deacon]

On Thu, 17 Apr 2025 11:47:54 +0000, Kornel Dulęba wrote:
> 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.
> 
> [...]

Applied to arm64 (for-next/mm), thanks!

[1/1] arm64: Support ARM64_VA_BITS=52 when setting ARCH_MMAP_RND_BITS_MAX
      https://git.kernel.org/arm64/c/f101c5644771

Cheers,
-- 
Will

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