Partially revert "arm64/mm: drop HAVE_ARCH_PFN_VALID"

This partially reverts commit 16c9afc7.

Alex Bee reports a regression in 5.14 on their RK3328 SoC when
configuring the PL330 DMA controller:

 | ------------[ cut here ]------------
 | WARNING: CPU: 2 PID: 373 at kernel/dma/mapping.c:235 dma_map_resource+0x68/0xc0
 | Modules linked in: spi_rockchip(+) fuse
 | CPU: 2 PID: 373 Comm: systemd-udevd Not tainted 5.14.0-rc7 #1
 | Hardware name: Pine64 Rock64 (DT)
 | pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
 | pc : dma_map_resource+0x68/0xc0
 | lr : pl330_prep_slave_fifo+0x78/0xd0

This appears to be because dma_map_resource() is being called for a
physical address which does not correspond to a memory address yet does
have a valid 'struct page' due to the way in which the vmemmap is
constructed.

Prior to 16c9afc7 ("arm64/mm: drop HAVE_ARCH_PFN_VALID"), the arm64
implementation of pfn_valid() called memblock_is_memory() to return
'false' for such regions and the DMA mapping request would proceed.
However, now that we are using the generic implementation where only the
presence of the memory map entry is considered, we return 'true' and
erroneously fail with DMA_MAPPING_ERROR because we identify the region
as DRAM.

Although fixing this in the DMA mapping code is arguably the right fix,
it is a risky, cross-architecture change at this stage in the cycle. So
just revert arm64 back to its old pfn_valid() implementation for v5.14.
The change to the generic pfn_valid() code is preserved from the original
patch, so as to avoid impacting other architectures.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Reported-by: Alex Bee <knaerzche@gmail.com>
Link: https://lore.kernel.org/r/d3a3c828-b777-faf8-e901-904995688437@gmail.comSigned-off-by: Will Deacon <will@kernel.org>

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);