linux-kernel - RE: [PATCH] x86/split_lock: Zap the unwieldy switch-case in sld_state

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Message-ID: <SJ1PR11MB6083BFCB1FFCE6DFE6F40D38FC84A@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Wed, 7 Jan 2026 16:41:22 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: Borislav Petkov <bp@...en8.de>, "Li, Xiaoyao" <xiaoyao.li@...el.com>
CC: Rong Zhang <i@...g.moe>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
	<mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	"x86@...nel.org" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, "Fenghua
 Yu" <fenghuay@...dia.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] x86/split_lock: Zap the unwieldy switch-case in
 sld_state_show()

> > For fatal mode, there is no such handling of temporarily disabling the
> > feature and we don't need the CPU offline callback.
>
> Yah, I got that. But why?
>
> Why is fatal mode different?
>
> Why does it matter what the split lock mode is when we offline CPUs?

It matters because the mode is shared by both hyper-threads, and you may
only offline one of them.

The offline handler isn't needed in the fatal case because split lock is
always enabled. So the "Unconditionally re-enable detection here."
won't change anything.

That said, it wouldn't break anything to run that. So if it makes the setup
code easier to read, it's OK to do this. But should have a comment to
describe what it going on.

-Tony