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SubjectRe: [PATCH v2] x86: mm: Do not use set_{pud,pmd}_safe when splitting the large page
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On 4/15/19 11:14 AM, Peter Zijlstra wrote:
> On Mon, Apr 15, 2019 at 08:58:52AM -0700, Dave Hansen wrote:
>> On 4/15/19 7:55 AM, Singh, Brijesh wrote:
>>> static unsigned long __meminit
>>> phys_pte_init(pte_t *pte_page, unsigned long paddr, unsigned long paddr_end,
>>> - pgprot_t prot)
>>> + pgprot_t prot, bool safe)
>>> {
>>> unsigned long pages = 0, paddr_next;
>>> unsigned long paddr_last = paddr_end;
>>> @@ -432,7 +463,7 @@ phys_pte_init(pte_t *pte_page, unsigned long paddr, unsigned long paddr_end,
>>> E820_TYPE_RAM) &&
>>> !e820__mapped_any(paddr & PAGE_MASK, paddr_next,
>>> E820_TYPE_RESERVED_KERN))
>>> - set_pte_safe(pte, __pte(0));
>>> + __set_pte(pte, __pte(0), safe);
>>> continue;
>>> }
>>
>> The changelog is great, btw.
>>
>> But, I'm not a big fan of propagating the 'safe' nomenclature. Could
>> we, at least, call it 'overwrite_safe' or something if we're going to
>> have a variable name? Or even, 'new_entries_only' or something that
>> actually conveys meaning?
>>
>> Because, just reading it, I always wonder "why do we have an unsafe
>> variant, that's stupid" every time. :)
>
> s/safe/init/ on the whole thing?
>

I will update the variable name in v3.

> And maybe even back on the initial _safe functions? Because all of this
> is about initializing page-tables, which is a TLB *safe* operation I
> suppose :-)
>

Since this particular patch need to pulled into stable hence I am
leaning towards making the _safe function rename after this patch.

>>> +#define DEFINE_ENTRY(type1, type2, safe) \
>>> +static inline void __set_##type1(type1##_t *arg1, \
>>> + type2##_t arg2, bool safe) \
>>> +{ \
>>> + if (safe) \
>>> + set_##type1##_safe(arg1, arg2); \
>>> + else \
>>> + set_##type1(arg1, arg2); \
>>> +}
>>
>> While I appreciate the brevity that these macros allow, I detest their
>> ability to thwart cscope and grep. I guess it's just one file, but it
>> does make me grumble a bit.
>
> There is scripts/tags.sh where you can add to regex_c to teach
> cscope/ctags about magic macros.
>
>> Also, can we do better than "__"? Aren't these specific to
>> initialization, and only for the kernel? Maybe we should call them
>> meminit_set_pte() or kern_set_pte() or something so make it totally
>> clear to the reader that they're new.
>
> set_*_init() and set_*() I suppose.
>

Will do

>>
>>> - kernel_physical_mapping_init(__pa(vaddr & pmask),
>>> - __pa((vaddr_end & pmask) + psize),
>>> - split_page_size_mask);
>>> + kernel_physical_mapping_change(__pa(vaddr & pmask),
>>> + __pa((vaddr_end & pmask) + psize),
>>> + split_page_size_mask);
>>
>> BTW, this hunk is really nice the way that the new naming makes it more
>> intuitive what's going on. My only nit w9uld be that we now have two
>> very similarly-named functions with different TLB-flushing requirements.
>>
>> Could we please include a comment at this site that reminds us that we
>> owe a TLB flush after this?
>
> Right, a comment would be good. I think my initial proposal had the TLB
> flushing inside, but I see the usage is in a loop, so I appreciate the
> desire to keep the TLB flushing outside.
>

I've add comment in kernel_physical_mapping_change() definition. I will
add something along that line here as well.

thanks
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