From: Catalin Marinas <catalin.marinas@arm.com>
To: Iurii Trukhin <yuri@trukhin.com>
Cc: Will Deacon <will@kernel.org>, Kees Cook <kees@kernel.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Ryan Roberts <ryan.roberts@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] arm64: raise default ARCH_MMAP_RND_BITS for 48-bit and 52-bit VA
Date: Thu, 15 Oct 2026 17:35:00 +0100 [thread overview]
Message-ID: <atEAtHiHh0eeVPn3@arm.com> (raw)
In-Reply-To: <CAOx7e9K5sgNcWNj4CemyZd0Ar1ZjR4o44B4nryohq-Ue6TNdKA@mail.gmail.com>
On Wed, Oct 14, 2026 at 10:23:35PM -0700, Iurii Trukhin wrote:
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index cab741a695f5..7bca47269dd5 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -313,6 +313,14 @@ config ARCH_MMAP_RND_BITS_MAX
> default 16 if ARM64_16K_PAGES
> default 18
>
> +# default to 1 TiB (5 bits below ARCH_MMAP_RND_BITS_MAX) on 48-bit and
> +# 52-bit VA; smaller VA sizes fall back to ARCH_MMAP_RND_BITS_MIN in
> +# arch/Kconfig
> +config ARCH_MMAP_RND_BITS
> + default 24 if (ARM64_VA_BITS=48 || ARM64_VA_BITS=52) && ARM64_64K_PAGES
> + default 26 if (ARM64_VA_BITS=48 || ARM64_VA_BITS=52) && ARM64_16K_PAGES
> + default 28 if (ARM64_VA_BITS=48 || ARM64_VA_BITS=52)
This looks fine but I was wondering what ARCH_MMAP_RND_BITS_DEFAULT (and
the compat equivalent) is for. It turns out that an int always evaluates
to 'n', so not taken into account. It might be worth removing them
altogether as a separate patch. No-one seems to be using them.
--
Catalin
next prev parent reply other threads:[~2026-10-15 16:35 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-15 5:23 [PATCH v2] arm64: raise default ARCH_MMAP_RND_BITS for 48-bit and 52-bit VA Iurii Trukhin
2026-10-15 13:32 ` Anshuman Khandual
2026-10-15 16:35 ` Catalin Marinas [this message]
2026-10-15 18:12 ` Catalin Marinas
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