Re: [PATCH v2] x86: Clear feature bits disabled at compile-time

[Maciej Wieczor-Retman]

On 2025-07-23 at 08:28:32 -0700, H. Peter Anvin wrote:
>On July 23, 2025 8:13:07 AM PDT, Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx> wrote:
>>On 2025-07-23 at 15:46:40 +0200, Borislav Petkov wrote:
>>>On Wed, Jul 23, 2025 at 11:22:49AM +0200, Maciej Wieczor-Retman wrote:
>>>> +static __init void init_cpu_cap(struct cpuinfo_x86 *c)
>>>> +{
>>>> +	int i;
>>>> +
>>>> +	for (i = 0; i < NCAPINTS; i++) {
>>>> +		cpu_caps_set[i] = REQUIRED_MASK(i);
>>>> +		cpu_caps_cleared[i] = DISABLED_MASK(i);
>>>> +	}
>>>> +}
>>>
>>>There's already apply_forced_caps(). Not another cap massaging function
>>>please. Add that stuff there.
>>
>>I'll try that, but can't it overwrite some things? apply_forced_caps() is called
>>three times and cpu_caps_set/cleared are modified in between from what I can
>>see. init_cpu_cap() was supposed to only initialize these arrays.
>>
>What are you concerned it would overwrite? I'm confused.

I thought that cpu_caps_set/cleared could change in-between apply_forced_caps()
calls. Therefore if we also applied the DISABLED_MASK() in every
apply_forced_caps() call I thought it might clear some flag that other function
might set.

But I've been looking at these calls for a while now and that doesn't seem
possible. Changes are made only if features are compiled, so it doesn't
interfere with the DISABLED_MASK().

Sorry for the confusion.

-- 
Kind regards
Maciej Wieczór-Retman