linux-kernel - Re: General protection fault in `switch_mm_irqs

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Date:   Wed, 9 Jan 2019 14:35:57 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Kosina <jikos@...nel.org>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Lendacky <Thomas.Lendacky@....com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: General protection fault in `switch_mm_irqs_off()`

Dear Thomas,


On 01/09/19 14:16, Thomas Gleixner wrote:

> On Wed, 9 Jan 2019, Paul Menzel wrote:
>> I get the same with microcode updates applied.
>>
>>     $ dmesg | grep 'microcode: CPU0: patch_level'
>>     [    3.809210] microcode: CPU0: patch_level=0x0600063e
>>     $ sudo modprobe msr
>>     $ sudo ./wrmsr 0x49 0x1
>>     wrmsr: CPU 0 cannot set MSR 0x00000049 to 0x0000000000000001
>>
>>> Could you please post /proc/cpuinfo from such a boot as well?
> 
> /proc/cpuinfo unfortunately does not contain the amd specific IBPB flag,
> but the dmesg of the original report says:
> 
>   Spectre V2 : mitigation: Enabling conditional Indirect Branch Prediction Barrier
> 
> which means, that the CPUID bit is set.
> 
> Can you please provide the output of:
> 
>   cpuid -1 -l 0x80000008 -r
> 
> On my AMD Opteron(TM) Processor 6276 with microcode 0x600063d loaded I get:
> 
>    0x80000008 0x00: eax=0x00003030 ebx=0x00000000 ecx=0x0000500f edx=0x00000000
> 
> EBX is 0, which means that X86_FEATURE_AMD_IBPB is not enabled. So the
> kernel does not try to use the speculation control MSR (0x49).

With CPUID 20180519, I get the output below with both microcode update versions.

0x600063d:

    $ sudo ./cpuid -1 -l 0x80000008 -r
    CPU:
       0x80000008 0x00: eax=0x00003030 ebx=0x00000000 ecx=0x0000500f edx=0x00000000

0x600063e:

    $ sudo ./cpuid -1 -l 0x80000008 -r
    CPU:
       0x80000008 0x00: eax=0x00003030 ebx=0x00000000 ecx=0x0000500f edx=0x00000000


Kind regards,

Paul


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