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

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Message-ID: <YgwAHU7gCnik8Kv6@zn.tnic>
Date:   Tue, 15 Feb 2022 20:33:49 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        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 Tue, Feb 15, 2022 at 10:19:31AM -0800, Pawan Gupta wrote:
> I admit it has gotten complicated with so many bits associated with TSX.

Yah, and looka here:

https://github.com/andyhhp/xen/commit/ad9f7c3b2e0df38ad6d54f4769d4dccf765fbcee

It seems it isn't complicated enough. ;-\

Andy just made me aware of this thing where you guys have added a new
MSR bit:

MSR_MCU_OPT_CTRL[1] which is called something like
MCU_OPT_CTRL_RTM_ALLOW or so. And lemme quote from that patch:

            /*
             * Probe for the February 2022 microcode which de-features TSX on
             * TAA-vulnerable client parts - WHL-R/CFL-R.
             *
             * RTM_ALWAYS_ABORT (read above) enumerates the new functionality,
             * but is read as zero if MCU_OPT_CTRL.RTM_ALLOW has been set
             * before we run.  Undo this.
             */

so MCU_OPT_CTRL.RTM_ALLOW=1 would have
CPUID.X86_FEATURE_RTM_ALWAYS_ABORT=0, which means, we cannot tie TSX disabling on
X86_FEATURE_RTM_ALWAYS_ABORT only.

So this would need more work, it seems to me.

Thx.

-- 
Regards/Gruss,
    Boris.

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