Re: [PATCH 5/6] x86/cpu-policy: Disentangle X86_NR_FEAT and FEATURESET_NR_ENTRIES

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.05.2023 22:13, Andrew Cooper wrote:
> On 09/05/2023 3:24 pm, Jan Beulich wrote:
>> On 09.05.2023 16:03, Andrew Cooper wrote:
>>> On 08/05/2023 8:45 am, Jan Beulich wrote:
>>>> On 04.05.2023 21:39, Andrew Cooper wrote:
>>>>> When adding new words to a featureset, there is a reasonable amount of
>>>>> boilerplate and it is preforable to split the addition into multiple 
>>>>> patches.
>>>>>
>>>>> GCC 12 spotted a real (transient) error which occurs when splitting 
>>>>> additions
>>>>> like this.  Right now, FEATURESET_NR_ENTRIES is dynamically generated 
>>>>> from the
>>>>> highest numeric XEN_CPUFEATURE() value, and can be less than what the
>>>>> FEATURESET_* constants suggest the length of a featureset bitmap ought to 
>>>>> be.
>>>>>
>>>>> This causes the policy <-> featureset converters to genuinely access
>>>>> out-of-bounds on the featureset array.
>>>>>
>>>>> Rework X86_NR_FEAT to be related to FEATURESET_* alone, allowing it
>>>>> specifically to grow larger than FEATURESET_NR_ENTRIES.
>>>>>
>>>>> Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>> While, like you, I could live with the previous patch even if I don't
>>>> particularly like it, I'm not convinced of the route you take here.
>>> It's the route you tentatively agreed to in
>>> https://lore.kernel.org/xen-devel/a282c338-98ab-6c3f-314b-267a5a82bad1@xxxxxxxx/
>> Right. Yet I deliberately said "may be the best" there, as something
>> better might turn up. And getting the two numbers to always agree, as
>> suggested, might end up being better.
> 
> Then don't write "yes" if what you actually mean is "I'd prefer a
> different option if possible", which is a "no".
> 
> I cannot read your mind, and we both know I do not have time to waste on
> this task.
> 
> And now I have to go and spend yet more time doing it differently.

I'm sorry for that. Yet please also allow for me to re-consider an earlier
voiced view, once I see things in more detail.

Jan