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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrVuW_MmksnkprK5Ljm-5RBSS=FUA8R8fgGMhZ3BxW15Sw@mail.gmail.com>
Date: Mon, 13 Oct 2025 13:32:30 -0700
From: Andy Lutomirski <luto@...nel.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Andy Lutomirski <luto@...nel.org>, 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>, 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 Mon, Oct 13, 2025 at 12:45 PM H. Peter Anvin <hpa@...or.com> wrote:
>
> 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.

The global timestamp would just be some field in the vvar area, which
we have plenty of anyway.

But I agree, accelerating getcpu is pointless.  In any case, anything
that historically thought it really really wanted accelerated getcpu
can, and probably does, use rseq these days.

--Andy