linux-kernel - Re: [v4.17-rcx] Lost IBPB, IBRS_FW support for spectre

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Date:   Tue, 1 May 2018 16:07:36 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Jörg Otte <jrg.otte@...il.com>
Cc:     kirill.shutemov@...ux.intel.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [v4.17-rcx] Lost IBPB, IBRS_FW support for spectre_v2 mitigation.



On 05/01/2018 11:27 AM, Thomas Gleixner wrote:
> On Tue, 1 May 2018, Thomas Gleixner wrote:
>> On Tue, 1 May 2018, Jörg Otte wrote:
>>> 2018-04-30 21:53 GMT+02:00 Thomas Gleixner <tglx@...utronix.de>:
>>>> --- a/arch/x86/kernel/cpu/common.c
>>>> +++ b/arch/x86/kernel/cpu/common.c
>>>> @@ -848,6 +848,11 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
>>>>                 c->x86_power = edx;
>>>>         }
>>>>
>>>> +       if (c->extended_cpuid_level >= 0x80000008) {
>>>> +               cpuid(0x80000008, &eax, &ebx, &ecx, &edx);
>>>> +               c->x86_capability[CPUID_8000_0008_EBX] = ebx;
>>>> +       }
>>>> +
>>>>         if (c->extended_cpuid_level >= 0x8000000a)
>>>>                 c->x86_capability[CPUID_8000_000A_EDX] = cpuid_edx(0x8000000a);
>>>>
>>>
>>> No, does not fix it.
>>
>> Then I really have no idea how reverting the patch you pointed out would
>> fix it.
> 
> Can you please carefully recheck:
> 
> 1) rc3 with d94a155c59c9 reverted.


I saw the same issue that Jorg Otte reported on a coffee lake system
with vanilla 4.17-rc3.
Reverting d94a155c59c9 did the trick for me.

Thanks.

Tim

> 
> 2) rc3 with the above patch applied.
> 
> If #1 works then #2 must work as well.
> 
> Thanks,
> 
> 	tglx
>