Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 fix from Will Deacon:
 "We received a report this week that the generic version of
  pfn_valid(), which we switched to this merge window in 16c9afc7
  ("arm64/mm: drop HAVE_ARCH_PFN_VALID"), interacts badly with
  dma_map_resource() due to the following check:

        /* Don't allow RAM to be mapped */
        if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
                return DMA_MAPPING_ERROR;

  Since the ongoing saga to determine the semantics of pfn_valid() is
  unlikely to be resolved this week (does it indicate valid memory, or
  just the presence of a struct page, or whether that struct page has
  been initialised?), just revert back to our old version of pfn_valid()
  for 5.14.

  Summary:

   - Fix dma_map_resource() by reverting back to old pfn_valid() code"

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  Partially revert "arm64/mm: drop HAVE_ARCH_PFN_VALID"

arch/arm64/Kconfig

@@ -156,6 +156,7 @@ config ARM64
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
+	select HAVE_ARCH_PFN_VALID
 	select HAVE_ARCH_PREL32_RELOCATIONS
 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
 	select HAVE_ARCH_SECCOMP_FILTER

arch/arm64/include/asm/page.h

@@ -41,6 +41,7 @@ void tag_clear_highpage(struct page *to);
 
 typedef struct page *pgtable_t;
 
+int pfn_valid(unsigned long pfn);
 int pfn_is_map_memory(unsigned long pfn);
 
 #include <asm/memory.h>

arch/arm64/mm/init.c

@@ -219,6 +219,43 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 	free_area_init(max_zone_pfns);
 }
 
+int pfn_valid(unsigned long pfn)
+{
+	phys_addr_t addr = PFN_PHYS(pfn);
+	struct mem_section *ms;
+
+	/*
+	 * 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;
+
+	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
+		return 0;
+
+	ms = __pfn_to_section(pfn);
+	if (!valid_section(ms))
+		return 0;
+
+	/*
+	 * ZONE_DEVICE memory does not have the memblock entries.
+	 * memblock_is_map_memory() check for ZONE_DEVICE based
+	 * addresses will always fail. Even the normal hotplugged
+	 * memory will never have MEMBLOCK_NOMAP flag set in their
+	 * memblock entries. Skip memblock search for all non early
+	 * memory sections covering all of hotplug memory including
+	 * both normal and ZONE_DEVICE based.
+	 */
+	if (!early_section(ms))
+		return pfn_section_valid(ms, pfn);
+
+	return memblock_is_memory(addr);
+}
+EXPORT_SYMBOL(pfn_valid);
+
 int pfn_is_map_memory(unsigned long pfn)
 {
 	phys_addr_t addr = PFN_PHYS(pfn);