linux-kernel - Re: [PATCH v4 0/3] Fix bugs and performance of kstack offset randomisation

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Message-ID: <20fb97f1-7e50-485a-bdfd-a2901d20ec84@intel.com>
Date: Mon, 19 Jan 2026 08:00:00 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Ryan Roberts <ryan.roberts@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Huacai Chen <chenhuacai@...nel.org>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Paul Walmsley <pjw@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Kees Cook <kees@...nel.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Arnd Bergmann <arnd@...db.de>, Mark Rutland <mark.rutland@....com>,
 "Jason A. Donenfeld" <Jason@...c4.com>, Ard Biesheuvel <ardb@...nel.org>,
 Jeremy Linton <jeremy.linton@....com>,
 David Laight <david.laight.linux@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 loongarch@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org,
 linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 0/3] Fix bugs and performance of kstack offset
 randomisation

On 1/19/26 05:01, Ryan Roberts wrote:
> x86 (AWS Sapphire Rapids):
> +-----------------+--------------+-------------+---------------+
> | Benchmark       | Result Class |   v6.18-rc5 | per-task-prng |
> |                 |              | rndstack-on |               |
> |                 |              |             |               |
> +=================+==============+=============+===============+
> | syscall/getpid  | mean (ns)    |  (R) 13.32% |     (R) 4.60% |
> |                 | p99 (ns)     |  (R) 13.38% |    (R) 18.08% |
> |                 | p99.9 (ns)   |      16.26% |    (R) 19.38% |

Like you noted, this is surprising. This would be a good thing to make
sure it goes in very early after -rc1 and gets plenty of wide testing.

But I don't see any problems with the approach, and the move to common
code looks like a big win as well:

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>