Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

From: Dave Hansen
Date: Mon Feb 04 2019 - 18:24:26 EST

On 2/4/19 1:40 PM, Borislav Petkov wrote:
>> Then, for the weirdo deployments where this feature is not enumerated,
>> we have the setcpuid= to fake the enumeration in software.
>> The reason I'm pushing for setcpuid= instead of a one-off is that I
>> don't expect this to be the last time Intel does this. I'd rather have
>> one setcpuid= than a hundred things like "ac_split_lock_disable".
> So my only issue with this is the user having to type this in in order
> to get the feature.
> VS
> automatically enabling it during boot in early_init_intel() or so. No
> need for any user intervention. It'll be just like a forgotten CPUID bit
> and we've done those before.

Actually, there's one part of all this that I forgot. Will split lock
detection be enumerated _widely_? IOW, will my laptop in 5 years
enumerate support for it? If so, we surely don't want to enable this
everyhwhere: it will break old apps. Doesn't that mean that we need
both feature detection and another separate bit for folks to opt-in?