On 1/9/19 8:34 AM, Paul Menzel wrote: > Dear Thomas, > > > On 01/09/19 15:29, Lendacky, Thomas wrote: >> On 1/9/19 7:35 AM, Paul Menzel wrote: > >>> 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 >> >> Hmmm... so ebx is 0 for both versions, so I'm not sure how IBPB is being >> set. What's the CPUID output for 0x07 (cpuid -1 -l 0x07 -r)? > > $ sudo ./cpuid -1 -l 0x07 -r > CPU: > 0x00000007 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 > edx=0x00000000
I'm confused then... the only way that I can see that the IBPB feature can be set is if 0x80000008[EBX] bit 12 is set or if 0x07[EDX] bit 26 is set - neither of which is the case. I must be missing something... Thanks, Tom > > > Kind regards, > > Paul >
