Re: General protection fault in `switch_mm_irqs_off()`

Paul Menzel
2019-01-09T13:36:01Z

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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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