Re: [PATCH] x86/tsx: Use MSR_TSX_CTRL to clear CPUID bits

From: Borislav Petkov <bp@alien8.de>
To: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Andi Kleen <ak@linux.intel.com>, Tony Luck <tony.luck@intel.com>,
	linux-kernel@vger.kernel.org,
	antonio.gomez.iglesias@linux.intel.com,
	neelima.krishnan@intel.com, stable@vger.kernel.org
Subject: Re: [PATCH] x86/tsx: Use MSR_TSX_CTRL to clear CPUID bits
Date: Tue, 15 Feb 2022 20:33:49 +0100	[thread overview]
Message-ID: <YgwAHU7gCnik8Kv6@zn.tnic> (raw)
In-Reply-To: <20220215181931.wxfsn2a3npg7xmi2@guptapa-mobl1.amr.corp.intel.com>

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