On Tue, May 1, 2018 at 5:59 AM Thomas Gleixner <t...@linutronix.de> wrote:
> Then I really have no idea how reverting the patch you pointed out would
> fix it.
So I do think that the original patch is buggy.
What I think *may* be going on is:
- first we do that
get_cpu_cap(c);
get_cpu_address_sizes(c);
but at that point, CPU levels may be masked, and that 0x80000008 leaf
isn't seen
- then we do
if (this_cpu->c_early_init)
this_cpu->c_early_init(c);
which calls early_init_intel(), which does that
if (msr_clear_bit(MSR_IA32_MISC_ENABLE,
MSR_IA32_MISC_ENABLE_LIMIT_CPUID_BIT) >
0) {
which now raises the cpuid_level.
- then we do
get_cpu_cap(c);
again, because the cpuid level has been raised, and _now_ it used to get
that 0x80000008 leaf information.
But with the change, that second call to get_cpu_cap() didn't do anything,
because the 0x80000008 leaf handling had been moved away.
However, I agree that your patch to just do that CPUID_8000_0008_EBX in
get_cpu_cap() should have fixed it, and it's possible that Jörg mis-tested
it.
Jörg, are you sure you didn't somehow get the wrong microcode? Because
another way for those bits to be cleared again is if
bad_spectre_microcode() triggers. That should show up in dmesg as "Intel
Spectre v2 broken microcode detected" though.
Linus
