linux-kernel - Re: [PATCH v2 1/2] cpu: Re-enable CPU mitigations by default for !X86 architectures

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Date: Tue, 23 Apr 2024 22:38:06 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: 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,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Michael Ellerman <mpe@...erman.id.au>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Will Deacon <will@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 1/2] cpu: Re-enable CPU mitigations by default for
 !X86 architectures

On Fri, Apr 19, 2024 at 05:05:54PM -0700, Sean Christopherson wrote:
> Rename x86's to CPU_MITIGATIONS, define it in generic code, and force it
> on for all architectures exception x86.  A recent commit to turn
> mitigations off by default if SPECULATION_MITIGATIONS=n kinda sorta missed
> that "cpu_mitigations" is completely generic, whereas
> SPECULATION_MITIGATIONS is x86 specific.
> 
> Rename x86's SPECULATIVE_MITIGATIONS instead of keeping both and have it
> select CPU_MITIGATIONS, as having two configs for the same thing is
> unnecessary and confusing.  This will also allow x86 to use the knob to
> manage mitigations that aren't strictly related to speculative execution.
> 
> Use another Kconfig to communicate to common code that CPU_MITIGATIONS is
> already defined instead of having x86's menu depend on the common
> CPU_MITIGATIONS.  This allows keeping a single point of contact for all of
> x86's mitigations, and it's not clear that other architectures *want* to
> allow disabling mitigations at compile-time.
> 
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Reported-by: Michael Ellerman <mpe@...erman.id.au>
> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Closes: https://lkml.kernel.org/r/20240413115324.53303a68%40canb.auug.org.au
> Fixes: f337a6a21e2f ("x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n")
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>

-- 
Josh