Re: [PATCH 2/2] arm64/mm: Reorganize pfn_valid()

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 1/29/21 3:37 PM, David Hildenbrand wrote:
> On 29.01.21 08:39, Anshuman Khandual wrote:
>> There are multiple instances of pfn_to_section_nr() and __pfn_to_section()
>> when CONFIG_SPARSEMEM is enabled. This can be just optimized if the memory
>> section is fetched earlier. Hence bifurcate pfn_valid() into two different
>> definitions depending on whether CONFIG_SPARSEMEM is enabled. Also replace
>> the open coded pfn <--> addr conversion with __[pfn|phys]_to_[phys|pfn]().
>> This does not cause any functional change.
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Ard Biesheuvel <ardb@kernel.org>
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>>   arch/arm64/mm/init.c | 38 +++++++++++++++++++++++++++++++-------
>>   1 file changed, 31 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 1141075e4d53..09adca90c57a 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -217,18 +217,25 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
>>       free_area_init(max_zone_pfns);
>>   }
>>   +#ifdef CONFIG_SPARSEMEM
>>   int pfn_valid(unsigned long pfn)
>>   {
>> -    phys_addr_t addr = pfn << PAGE_SHIFT;
>> +    struct mem_section *ms = __pfn_to_section(pfn);
>> +    phys_addr_t addr = __pfn_to_phys(pfn);
> 
> I'd just use PFN_PHYS() here, which is more frequently used in the kernel.

Sure, will replace.

> 
>>   -    if ((addr >> PAGE_SHIFT) != pfn)
>> +    /*
>> +     * Ensure the upper PAGE_SHIFT bits are clear in the
>> +     * pfn. Else it might lead to false positives when
>> +     * some of the upper bits are set, but the lower bits
>> +     * match a valid pfn.
>> +     */
>> +    if (__phys_to_pfn(addr) != pfn)
> 
> and here PHYS_PFN(). Comment is helpful. :)

Sure, will replace.

> 
>>           return 0;
>>   -#ifdef CONFIG_SPARSEMEM
>>       if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
>>           return 0;
>>   -    if (!valid_section(__pfn_to_section(pfn)))
>> +    if (!valid_section(ms))
>>           return 0;
>>         /*
>> @@ -240,11 +247,28 @@ int pfn_valid(unsigned long pfn)
>>        * memory sections covering all of hotplug memory including
>>        * both normal and ZONE_DEVICE based.
>>        */
>> -    if (!early_section(__pfn_to_section(pfn)))
>> -        return pfn_section_valid(__pfn_to_section(pfn), pfn);
>> -#endif
>> +    if (!early_section(ms))
>> +        return pfn_section_valid(ms, pfn);
>> +
>>       return memblock_is_map_memory(addr);
>>   }
>> +#else
>> +int pfn_valid(unsigned long pfn)
>> +{
>> +    phys_addr_t addr = __pfn_to_phys(pfn);
>> +
>> +    /*
>> +     * Ensure the upper PAGE_SHIFT bits are clear in the
>> +     * pfn. Else it might lead to false positives when
>> +     * some of the upper bits are set, but the lower bits
>> +     * match a valid pfn.
>> +     */
>> +    if (__phys_to_pfn(addr) != pfn)
>> +        return 0;
>> +
>> +    return memblock_is_map_memory(addr);
>> +}
> 
> 
> I think you can avoid duplicating the code by doing something like:

Right and also this looks more compact as well. Initially though about
it but then was apprehensive about the style in #ifdef { } #endif code
block inside the function. After this change, the resulting patch also
clears checkpatch.pl test. Will do the change.

> 
> 
> phys_addr_t addr = PFN_PHYS(pfn);
> 
> if (PHYS_PFN(addr) != pfn)
>     return 0;
> 
> #ifdef CONFIG_SPARSEMEM
> {
>     struct mem_section *ms = __pfn_to_section(pfn);
> 
>     if (!valid_section(ms))
>         return 0;
>     if (!early_section(ms))
>         return pfn_section_valid(ms, pfn);
> }
> #endif
> return memblock_is_map_memory(addr);
>