Re: [PATCH RESEND v2 3/3] x86/cpu: Enable modifying bug flags with {clear,set}puid

[Brendan Jackman]

On Mon, 17 Feb 2025 at 18:08, Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Mon, Feb 17, 2025 at 05:56:32PM +0100, Brendan Jackman wrote:
> > Er, hold on, what chunk can be whacked? Do you mean delete the ability
> > to set clearcpuid by number? There are still features with no name.
>
> Really, which ones?

I just mean the ones without a "name" in cpufeatures.h, e.g.

#define X86_FEATURE_MSR_SPEC_CTRL ( 7*32+16) /* MSR SPEC_CTRL is implemented */

> Are you saying you want to turn off *arbitrary* features? Not only what gets
> advertized in /proc/cpuinfo?

You can already clear arbitrary ones with clearcpuid.

But for bugs, they all have a name. I was thinking that this was
because they are defined by the kernel, that's what I meant by "It t
doesn't make sense for a bug not to have a name", although now I think
about it we could totally have a bug and not give it a user-visible
name if we wanted to.

Anyway, still think the current logic is what we want here:

- The new setcpuid should be consistent with the existing clearcpuid,
i.e. accept numbers for the same things clearcpuid does.

- There are currently no bugs without names so for those, require the
string for both setcpuid and clearcpuid. If we wanted to we could add
number support later.