linux-kernel - Re: [PATCH v2] vdso: Remove struct getcpu

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Message-ID: <9F23DEFF-FCD7-488E-B31C-E891A7521D9E@zytor.com>
Date: Mon, 13 Oct 2025 09:14:51 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Dave Hansen <dave.hansen@...el.com>,
        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>, Andy Lutomirski <luto@...nel.org>,
        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>
CC: 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 October 13, 2025 7:06:55 AM PDT, Dave Hansen <dave.hansen@...el.com> wrote:
>On 10/13/25 02:20, Thomas Weißschuh wrote:
>> -int __vdso_getcpu(unsigned int *cpu, unsigned int *node, struct getcpu_cache *unused);
>> -int __vdso_getcpu(unsigned int *cpu, unsigned int *node, struct getcpu_cache *unused)
>> +int __vdso_getcpu(unsigned int *cpu, unsigned int *node, void *unused);
>> +int __vdso_getcpu(unsigned int *cpu, unsigned int *node, void *unused)
>>  {
>>  	int cpu_id;
>
>It would ideally be nice to have a _bit_ more history on this about
>how it became unused any why there is such high confidence that
>userspace never tries to use it.
>
>Let's say someone comes along in a few years and wants to use this
>'unused' parameter. Could they?

I believe it was a private storage area for the kernel to use... which it doesn't. Not doing anything at all with the pointer is perfectly legitimate.