Re: [Patch V1 4/7] x86/microcode/core: Take a snapshot before and after applying microcode

[Borislav Petkov]

On Tue, Nov 29, 2022 at 01:08:29PM -0800, Ashok Raj wrote:
> The kernel caches features about each CPU's features at boot in an
> x86_capability[] structure. The microcode update takes one snapshot and
> compares it with the saved copy at boot.
> 
> However, the capabilities in the boot copy can be turned off as a result of
> certain command line parameters or configuration restrictions. This can
> cause a mismatch when comparing the values before and after the microcode
> update.

Hmm, but if that has happened, the capabilities will be turned off in
your @orig argument below?

Or are you saying that this copy_cpu_caps() read before the update will
overwrite the cleared bits with the their actual values from CPUID so
that what you really wanna compare here is *hardware* CPUID bits before
and after and not our potentially modified copy?

I.e., some bit in CPUID is 1 and we have cleared it in our copy.

Close?

If so, then this should be specifically called out in the commit
message.

> +static void copy_cpu_caps(struct cpuinfo_x86 *info)

If anything, that function should be called

store_cpu_caps()

and store it into its parameter *info.

-- 
Regards/Gruss,
    Boris.

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