Re: [PATCH] x86/msr: do not warn on writes to OC_MAILBOX

[Borislav Petkov]

Hi,

On Mon, Sep 07, 2020 at 12:46:35PM +0200, Jason A. Donenfeld wrote:
> Are you sure that intel-undervolt using OC_MAILBOX from userspace is
> actually a "misuse"? Should the kernel or kernel drivers actually be
> involved with the task of underclocking? This seems pretty squarely in
> the realm of "hobbyists poking and prodding at their CPUs" rather than
> something made for a kernel driver, right?

The only thing I'm sure is that *if* it makes sense for any driver to
control something in the hardware over MSRs, it should *not* poke at
naked MSRs but use a proper interface.

I'd leave it to the people who actually need this interface, to explain
why they do.

> Also, what was the justification for whitelisting
> MSR_IA32_ENERGY_PERF_BIAS?

That's:

tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c

Once that thing gets converted to a proper interface too, that MSR goes
off the allowlist too.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette