linux-kernel - Re: [PATCH] x86/tsx: Use MSR_TSX

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Date:   Tue, 15 Feb 2022 11:24:01 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
        antonio.gomez.iglesias@...ux.intel.com, neelima.krishnan@...el.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] x86/tsx: Use MSR_TSX_CTRL to clear CPUID bits

On Mon, Feb 14, 2022 at 04:20:14PM -0800, Pawan Gupta wrote:
> ... we are calling tsx_clear_cpuid() unconditionally.

I know, that's why I asked...

> > If those CPUs which support only disabling TSX through MSR_IA32_TSX_CTRL
> > but don't have MSR_TSX_FORCE_ABORT - if those CPUs set
> > X86_FEATURE_RTM_ALWAYS_ABORT too, then this should work.

... this^^.

IOW, what are you fixing here exactly?

Let's look at the two callsites of tsx_clear_cpuid():

1. tsx_init: that will do something on X86_FEATURE_RTM_ALWAYS_ABORT CPUs.

2. init_intel: that will get called when

	tsx_ctrl_state == TSX_CTRL_RTM_ALWAYS_ABORT

But TSX_CTRL_RTM_ALWAYS_ABORT gets set only when
X86_FEATURE_RTM_ALWAYS_ABORT is set. I.e., the first case, in
tsx_init().

So, IIUC, you wanna fix the case where CPUs which set
X86_FEATURE_RTM_ALWAYS_ABORT but *don't* have MSR_TSX_FORCE_ABORT, those
CPUs should still disable TSX through MSR_IA32_TSX_CTRL.

Correct?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette