From: Karl Mehltretter <kmehltretter@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: compat: Keep alignment address arithmetic 32-bit
Date: Wed, 19 Aug 2026 20:55:57 +0200 [thread overview]
Message-ID: <aoX6wpJjMS1vtlVY@gmail.com> (raw)
In-Reply-To: <4078f942-e29a-4f6f-b6fc-780e8c6d6874@app.fastmail.com>
On Wed, Aug 19, 2026 at 01:19:20PM +0100, Arnd Bergmann wrote:
>
> I don't see yet why 64K_PAGES makes a difference. I had
> expected TASK_SIZE to be 4GiB regardless of the page size, and
> the top page (but not the bottom page) to be reachable from normal
> userspace.
There is a special case in arch/arm64/include/asm/processor.h:
#if defined(CONFIG_ARM64_64K_PAGES) && defined(CONFIG_KUSER_HELPERS)
#define TASK_SIZE_32 UL(0x100000000)
#else
#define TASK_SIZE_32 (UL(0x100000000) - PAGE_SIZE)
#endif
Only ARM64_64K_PAGES with KUSER_HELPERS gives compat tasks the
full 4 GiB. The 64K kuser mapping then occupies the last
page.
I'll send a v2 soon.
Karl
next prev parent reply other threads:[~2026-08-19 18:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-17 0:02 Karl Mehltretter
2026-08-17 9:15 ` Arnd Bergmann
2026-08-18 3:22 ` Karl Mehltretter
2026-08-18 7:31 ` Arnd Bergmann
2026-08-19 4:56 ` Karl Mehltretter
2026-08-19 11:19 ` Arnd Bergmann
2026-08-19 18:55 ` Karl Mehltretter [this message]
2026-08-19 20:27 ` Arnd Bergmann
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