Re: [PATCH 1/7] x86/feature: Detect the x86 feature to control Speculation

Tom Lendacky
2018-01-05T15:14:50Z

On 1/5/2018 5:14 AM, David Woodhouse wrote:
> On Thu, 2018-01-04 at 09:56 -0800, Tim Chen wrote:
>> cpuid ax=0x7, return rdx bit 26 to indicate presence of this feature
>> IA32_SPEC_CTRL (0x48) and IA32_PRED_CMD (0x49)
>> IA32_SPEC_CTRL, bit0 – Indirect Branch Restricted Speculation (IBRS)
>> IA32_PRED_CMD,  bit0 – Indirect Branch Prediction Barrier (IBPB)
>
> In a previous iteration of these patches, hadn't you already merged
> support for the AMD variant? Where'd that go?

It looks like this series is strictly IBRS related. Even though some of
the IBPB definitions are in here, there isn't support later for indicating
IBPB is in use or any places where IBPB would be used. I was assuming that
there would be another series for IBPB support. Is that the plan?

AMD is covered by the IBRS support as is, but we also have support for
the IBPB feature alone, identified by a different CPUID bit. I was
waiting for the IBPB series to see if I needed to submit anything or
whether the patches were included.

Thanks,
Tom

>