Re: [PATCH 2/5] x86/ucode: Fold early_update_cache() into microcode_init_cache()

[George Dunlap <dunlapg@xxxxxxxxx>]

On Tue, Mar 28, 2023 at 4:58 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:

On 28.03.2023 17:07, Andrew Cooper wrote:
> On 28/03/2023 2:51 pm, Jan Beulich wrote:
>> On 27.03.2023 21:41, Andrew Cooper wrote:
>>> It is not valid to retain a bootstrap_map() across returning back to
>>> __start_xen(), but various pointers get stashed across calls.
>> It's error prone, yes, but "not valid" isn't really true imo: As long as
>> nothing calls bootstrap_map(NULL) all mappings will remain as they are.
>
> And how is this code supposed to know whether it's stashed pointer is
> any good or not?
>
> This is precisely "not valid" means.  It doesn't mean "it definitely
> doesn't work", but very much does mean "can't rely on it working".

Hmm, not my understanding of "not valid".

A "valid" approach or algorithm is one which can be relied on.  If an approach or algorithm may sometimes work or may sometimes not work, it's not valid.

That said:

* "Not valid" is kind of vague: it tells you think it's "bad", but not how.  (Even "racy" or "risky" or "error-prone" are more descriptive, because it prompts you for the types of problems to think about.) It's usually better to state exactly what problems might happen if you do X, rather than simply saying X is "not valid".

* It's usually better to propose specific alternate wording, rather than arguing about whether a given wording is... er, valid or not. 

 -George