On 10/21/19 4:29 PM, speck for Pawan Gupta wrote:
> From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Subject: [PATCH v7 07/10] x86/tsx: Add "auto" option to TSX cmdline parameter
> 
> Platforms which are not affected by X86_BUG_TAA may want the TSX feature
> enabled. Add "auto" option to the TSX cmdline parameter. When tsx=auto
> disable TSX when X86_BUG_TAA is present, otherwise enable TSX.

Earlier, you do this:

+	if (!(ia32_cap & ARCH_CAP_TAA_NO) &&
+	    (boot_cpu_has(X86_FEATURE_RTM) ||
+	     (ia32_cap & ARCH_CAP_TSX_CTRL_MSR)))
+		setup_force_cpu_bug(X86_BUG_TAA);

Per the other discussion, I think you want to double check if tsx=auto
is doing what folks want it to do, because currently I think auto still
has the semantics of turning off TSX on everything, rather than just
those cases where a VERW mitigation won't suffice/is in use.

(see Thomas's update to the "Re: [PATCH v5 08/11] TAAv5 8" diagram)

It seems that it's a good time to double check if that's what everyone
on the distro side is expecting, namely "tsx=auto will disable TSX
automatically on those parts impacted by TAA for which VERW mitigation
is not available". This seems to reduce the set where we end up
disabling TSX essentially to a few very recent processors (e.g.
CascadeLake some second gen, Bx stepping?). If that's what we are all
expecting/are planning to do, I suspect Red Hat would go with tsx=auto
as a default since the set of impacted processors can be documented.

Anyway, auto isn't right yet.

Jon.

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Computer Architect | Sent with my Fedora powered laptop