linux-kernel - Re: [PATCH v2 2/2] x86/tsx: Get the tsx= command line parameter with early

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Message-ID: <20251022183040.5b5731cb@mordecai>
Date: Wed, 22 Oct 2025 18:31:04 +0200
From: Petr Tesarik <ptesarik@...e.com>
To: Nikolay Borisov <nik.borisov@...e.com>, Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, "maintainer:X86
 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "open list:X86
 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] x86/tsx: Get the tsx= command line parameter
 with early_param()

On Wed, 8 Oct 2025 16:03:43 +0200
Petr Tesarik <ptesarik@...e.com> wrote:

> On Tue, 7 Oct 2025 15:50:02 +0300
> Nikolay Borisov <nik.borisov@...e.com> wrote:
> 
> > On 26.09.25 г. 21:01 ч., Petr Tesarik wrote:  
> > > Use early_param() to get the value of the tsx= command line parameter.
> > > Although cmdline_find_option() works fine, the option is later reported
> > > as unknown and passed to user space. The latter is not a real issue, but
> > > the former is confusing and makes people wonder if the tsx= parameter had
> > > any effect and double-check for typos unnecessarily.
> > > 
> > > The behavior changes slightly if "tsx" is given without any argument (which
> > > is invalid syntax). Prior to this patch, the kernel logged an error message
> > > and disabled TSX. With this patch, the parameter is ignored. The new
> > > behavior is consistent with other parameters, e.g. "tsx_async_abort".
> > > 
> > > Signed-off-by: Petr Tesarik <ptesarik@...e.com>    
> > 
> > LGTM, also could you include some rationale why early_param vs __setup 
> > for example, or arch_param_cb (which by the way has yet to find its 
> > first user).  
> 
> I'd love to, but I'm a noob myself, so I simply followed Borislav's
> advice here:
> 
> https://lore.kernel.org/all/20250915143909.GAaMglDd5oRSPDDuqu@fat_crate.local/
> 
> @Borislav: Would you mind explaining your request to use early_param()?

Never mind, I have spent some time on it, so here's a dump of how I
understand it:

https://sigillatum.tesarici.cz/2025-10-22-kernel-parameters.html

HTH
Petr T