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

On Tue, Oct 22, 2019 at 09:04:34PM +0200, speck for Borislav Petkov wrote:
> On Tue, Oct 22, 2019 at 10:44:52AM -0700, speck for Pawan Gupta wrote:
> > There is a small problem with this, it will set
> > 
> > 	taa_mitigation = TAA_MITIGATION_TSX_DISABLE;
> > 
> > when there is no X86_BUG_TAA.
> 
> And?
> 
> When the CPU doesn't support TSX, then this practically is "Mitigation:
> TSX disabled" because, well, TSX *is* disabled.

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.

> 
> 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");
		[...]

Thanks,
Pawan