Re: General protection fault in `switch_mm_irqs_off()`

Thomas Gleixner
2019-01-09T13:16:11Z

Paul,

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).

Thanks,

tglx