Re: [RFC PATCH] tools/x86: add kcpuid tool to show raw CPU features

[Dave Hansen]

On 9/2/20 9:45 AM, peterz@xxxxxxxxxxxxx wrote:
> On Thu, Aug 27, 2020 at 03:49:03PM +0800, Feng Tang wrote:
>> End users frequently want to know what features their processor
>> supports, independent of what the kernel supports.
>>
>> /proc/cpuinfo is great. It is omnipresent and since it is provided by
>> the kernel it is always as up to date as the kernel. But, it can be
>> ambiguous about processor features which can be disabled by the kernel
>> at boot-time or compile-time.
> 
> Let me once again suggest we use CPUID faulting to 'fix' this.
> 
> We really should clear the CPUID bits when the kernel explicitly
> disables things.
> 
> https://lkml.kernel.org/r/1552431636-31511-18-git-send-email-fenghua.yu@xxxxxxxxx

Wouldn't we also have to turn on faulting for all the bits that are
enumerated, but of which the kernel is unaware?

Right now, a bit that we clearcpuid= and one about which the kernel is
totally unaware look the same.