There are multiple instances of pfn_to_section_nr() and __pfn_to_section()
when CONFIG_SPARSEMEM is enabled. This can be optimized if memory section
is fetched earlier. This replaces the open coded PFN and ADDR conversion
with PFN_PHYS() and PHYS_PFN() helpers. While there, also add a comment.
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 <redacted>
---
  arch/arm64/mm/init.c | 20 +++++++++++++++-----
  1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 1141075e4d53..5d8fd5360a68 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c

@@ -219,16 +219,25 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
  
  int pfn_valid(unsigned long pfn)
  {
-	phys_addr_t addr = pfn << PAGE_SHIFT;
+	phys_addr_t addr = PFN_PHYS(pfn);
  
-	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_PFN(addr) != pfn)
  		return 0;
  
  #ifdef CONFIG_SPARSEMEM
+{
+	struct mem_section *ms = __pfn_to_section(pfn);
+
  	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
  		return 0;
  
-	if (!valid_section(__pfn_to_section(pfn)))
+	if (!valid_section(ms))
  		return 0;
  
  	/*

@@ -240,8 +249,9 @@ 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);
+	if (!early_section(ms))
+		return pfn_section_valid(ms, pfn);
+}
  #endif
  	return memblock_is_map_memory(addr);
  }