arm64/mm: Reorganize pfn_valid()

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
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/1614921898-4099-3-git-send-email-anshuman.khandual@arm.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/mm/init.c

@@ -219,16 +219,26 @@ 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;
+
 	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
 		return 0;
 
-	if (!valid_section(__pfn_to_section(pfn)))
+	ms = __pfn_to_section(pfn);
+	if (!valid_section(ms))
 		return 0;
 
 	/*
@@ -240,8 +250,9 @@ 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);
 }