linux-kernel - Re: [PATCH v2 08/13] sparc64: vdso: Switch to the generic vDSO library

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Message-Id: <6390486f-ccc7-4f77-8126-1e0b3b67bc75@app.fastmail.com>
Date: Mon, 01 Sep 2025 17:17:13 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>
Cc: "Andreas Larsson" <andreas@...sler.com>,
 "Andy Lutomirski" <luto@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>,
 "Vincenzo Frascino" <vincenzo.frascino@....com>,
 "David S . Miller" <davem@...emloft.net>,
 "Nagarathnam Muthusamy" <nagarathnam.muthusamy@...cle.com>,
 "Nick Alcock" <nick.alcock@...cle.com>, "John Stultz" <jstultz@...gle.com>,
 "Stephen Boyd" <sboyd@...nel.org>, linux-kernel@...r.kernel.org,
 sparclinux@...r.kernel.org
Subject: Re: [PATCH v2 08/13] sparc64: vdso: Switch to the generic vDSO library

On Fri, Aug 29, 2025, at 12:52, Thomas Weißschuh wrote:
> On Fri, Aug 29, 2025 at 12:40:59PM +0200, John Paul Adrian Glaubitz wrote:
>> On Fri, 2025-08-29 at 12:37 +0200, Thomas Weißschuh wrote:
>> > In the meantime I installed a full Debian, but the bug is still not
>> > reproducible in QEMU.
>> 
>> Please keep in mind that QEMU emulates sun4u (on UltraSPARC II) while
>> Andreas was testing on sun4v (on Niagara 4). There might be differences.
>
> I am aware. Unfortuntely I don't have anything else available.
> If anybody could test this on real sun4u that would be great.
> Or teach me how to use sun4v QEMU without it crashing on me.
> In the past you offered access to a physical machine.
> Does this offer still stand? Does it also run into the bug?

It should be enough to set the cpu to a different type. As far
as I can tell, the three different cases are all determined by the
MMU/CPU ID, not the platform type (sun4u/sun4v).

As far as I can tell, the options are:

- JPS1 (UltraSPARCIII, SPARC64 V) and later use modern 'stick' operations
- UltraSparc IIe (Hummingbird) uses 'hbtick' without VDSO
- All other plain V9 implementations use 'tick'

To test all three cases, it should be enough to run qemu with e.g.
"-cpu Sun-UltraSparc-IV", "-cpu TI-UltraSparc-IIe", and
"-cpu TI-UltraSparc-II", respectively.

       Arnd