[MODERATED] Re: [PATCH v7 04/10] TAAv7 4

On Tue, Oct 22, 2019 at 11:53:21PM +0200, Borislav Petkov wrote:
> On Tue, Oct 22, 2019 at 02:29:02PM -0700, speck for Pawan Gupta wrote:
> > Side effect of RTM check ahead of X86_BUG_TAA will be a dmesg print
> > "Mitigation: TSX disabled" when X86_BUG_TAA is not set.
> 
> So what you're trying to tell me is that you don't want to print that
> message at all?
> 
> 	if (!boot_cpu_has(X86_FEATURE_RTM)) {
> 		taa_mitigation = TAA_MITIGATION_TSX_DISABLE;
> 		return;
> 	}
> 
> How's that?

And to perhaps answer your other question from below maybe - I'm
assuming you want something like this:

	if (!boot_cpu_has(X86_FEATURE_RTM)) {
		taa_mitigation = TAA_MITIGATION_TSX_DISABLE;
		setup_clear_cpu_bug(X86_BUG_TAA);
		return;
	}

This is assuming X86_FEATURE_RTM really mirrors the CPUID bit. And that
should be the case since if you do tsx_disable(), it will clear the
CPUID bit through the MSR. IOW, when TSX is disabled, you're basically
not affected by TAA, of course.

> > > Also, from all the possible settings:
> > > 
> > >         [TAA_MITIGATION_OFF]            = "Vulnerable",
> > >         [TAA_MITIGATION_UCODE_NEEDED]   = "Vulnerable: Clear CPU buffers attempted, no microcode",
> > >         [TAA_MITIGATION_VERW]           = "Mitigation: Clear CPU buffers",
> > >         [TAA_MITIGATION_TSX_DISABLE]    = "Mitigation: TSX disabled",
> > > 
> > > TAA_MITIGATION_TSX_DISABLE is the one that fits best for the !RTM case,
> > > no?
> > 
> > When X86_BUG_TAA is not set sysfs shows "Not affected" irrespective of
> > value of taa_mitigation.
> > 
> > 	cpu_show_common()
> > 	{
> > 		if (!boot_cpu_has_bug(bug))
> > 			return sprintf(buf, "Not affected\n");
> > 		[...]
> 
> Sorry, I can't follow what you're trying to tell me here.

-- 
Regards/Gruss,
    Boris.

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