[MODERATED] Re: [PATCH 3/9] TAA 3

On Thu, Oct 24, 2019 at 02:59:59PM -0500, speck for Josh Poimboeuf wrote:
> But pre-TSX_CTRL CPUs won't reach the above code, because of the
> tsx_ctrl_is_supported() check at the beginning of tsx_init().

Yes, pre-TSX_CTRL won't have those CPUID bits cleared because they
cannot anyway - MSR is not there.

And even if we clear the corresponding X86_FEATURE_ bits, nothing is
stopping people from using TSX - they won't query /proc/cpuinfo but
CPUID directly. Hell, they can even try the instructions and see if they
fault or not, without querying any feature bits.

> And post-TSX_CTRL CPUs will have the HLE bit already cleared by
> microcode.

Yes.

In both cases, the X86_FEATURE_* bits mirror what's in CPUID. At least
for the two TSX bits: HLE and RTM.

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Regards/Gruss,
    Boris.

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