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

[David Hildenbrand <david@redhat.com>]

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.

>   
> -	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. :)

>   		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:


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);

-- 
Thanks,

David / dhildenb