Messages in this thread | | | From | Linus Torvalds <> | Date | Tue, 01 May 2018 20:14:37 +0000 | Subject | Re: [v4.17-rcx] Lost IBPB, IBRS_FW support for spectre_v2 mitigation. |
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On Tue, May 1, 2018 at 5:59 AM Thomas Gleixner <tglx@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
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