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Message-ID: <494caf29-8755-4bc6-a2c3-b9d0b3e9b78d@zytor.com>
Date: Mon, 13 Oct 2025 12:44:19 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...el.com>
Cc: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...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>, x86@...nel.org,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Johannes Berg <johannes@...solutions.net>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Shuah Khan
<shuah@...nel.org>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
linux-um@...ts.infradead.org, linux-api@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2] vdso: Remove struct getcpu_cache
On 2025-10-13 10:14, Andy Lutomirski wrote:
>
> I don't actually remember whether the kernel ever used this. It's
> possible that there are ancient kernels where passing a wild, non-null
> pointer would blow up. But it's certainly safe to pass null, and it's
> certainly safe for the kernel to ignore the parameter.
>
One could imagine an architecture which would have to execute an actual system
call wanting to use this, but on x86 it is pointless -- even the LSL trick is
much faster than a system call, and once you account for whatever hassle you
would have to deal with do make the cache make sense (probably having a global
generation number and/or a timestamp to expire it) it well and truly makes no
sense.
-hpa
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