Re: [PATCH v5 10/14] x86/mm: Simplify clear_page_*

[David Hildenbrand <david@redhat.com>]

On 11.07.25 19:26, Ankur Arora wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 10.07.25 02:59, Ankur Arora wrote:
>>> clear_page_rep() and clear_page_erms() are wrappers around "REP; STOS"
>>> variations. Inlining gets rid of an unnecessary CALL/RET (which isn't
>>> free when using RETHUNK speculative execution mitigations.)
>>> Fixup and rename clear_page_orig() to adapt to the changed calling
>>> convention.
>>> And, add a comment from Dave Hansen detailing various clearing mechanisms
>>> used in clear_page().
>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>> ---
>>>    arch/x86/include/asm/page_32.h |  6 +++++
>>>    arch/x86/include/asm/page_64.h | 42 ++++++++++++++++++++++++++--------
>>>    arch/x86/lib/clear_page_64.S   | 39 +++++++------------------------
>>>    3 files changed, 46 insertions(+), 41 deletions(-)
>>> diff --git a/arch/x86/include/asm/page_32.h b/arch/x86/include/asm/page_32.h
>>> index 0c623706cb7e..a8ff43bb9652 100644
>>> --- a/arch/x86/include/asm/page_32.h
>>> +++ b/arch/x86/include/asm/page_32.h
>>> @@ -17,6 +17,12 @@ extern unsigned long __phys_addr(unsigned long);
>>>      #include <linux/string.h>
>>>    +/*
>>
>> /** if this was supposed to be kernel doc (which it looks like it is)
>>
>>> + * clear_page() - clear kernel page.
>>
>> "clear a kernel page"
>>
>> Although I am not sure what a "kernel page" is.
>>
>> Did you mean "clear a page using a kernel virtual address" ?
> 
> Thanks. Yes, this makes way more sense.

FWIW, most clear_user_page() will just call clear_page(). The ones that 
don't, have to deal with the dcache flushing, as the page might have 
cache alias from another (mm) address space.

So clear_page() is just about clearing page content using a kernel 
virtual address, and clear_user_page() is additionally taking care of 
any dcache aliases.

-- 
Cheers,

David / dhildenb