Re: [PATCH v1 03/11] x86/mm/pat: introduce pfnmap_track() and pfnmap_untrack()

David Hildenbrand
2025-04-28T17:12:23Z

>>
>> +int pfnmap_track(unsigned long pfn, unsigned long size, pgprot_t *prot)
>> +{
>> + const resource_size_t paddr = (resource_size_t)pfn << PAGE_SHIFT;
>> +
>> + return reserve_pfn_range(paddr, size, prot, 0);
>
> Nitty, but a pattern established by Liam which we've followed consistently
> in VMA code is to prefix parameters that might be less than obvious,
> especially boolean parameters, with a comment naming the parameter, e.g.:
> > return reserve_pfn_range(paddr, size, prot, /*strict_prot=*/0);

Not sure I like that. But as this parameter goes away patch #8, I'll
leave it as is in this patch and not start a bigger discussion on better
alternatives (don't use these stupid boolean variables ...) ;)

[...]

>> +
>> +/**
>> + * pfnmap_track - track a pfn range
>
> To risk sounding annoyingly pedantic and giving the kind of review that is
> annoying, this really needs to be expanded, I think perhaps this
> description is stating the obvious :)
>
> To me the confusing thing is that the 'generic' sounding pfnmap_track() is
> actually PAT-specific, so surely the description should give a brief
> overview of PAT here, saying it's applicable on x86-64 etc. etc.
>
> I'm not sure there's much use in keeping this generic when it clearly is
> not at this point?

Sorry, is your suggestion to document more PAT stuff or what exactly?

As you know, I'm a busy man ... so instructions/suggestions please :)

>
>> + * @pfn: the start of the pfn range
>> + * @size: the size of the pfn range
>
> In what units? Given it's a pfn range it's a bit ambiguous as to whether it
> should be expressed in pages/bytes.

Agreed. It's bytes. (not my favorite here, but good enough)

--
Cheers,

David / dhildenb