arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory

[ Upstream commit eeb0753ba27b26f609e61f9950b14f1b934fe429 ]

pfn_valid() validates a pfn but basically it checks for a valid struct page
backing for that pfn. It should always return positive for memory ranges
backed with struct page mapping. But currently pfn_valid() fails for all
ZONE_DEVICE based memory types even though they have struct page mapping.

pfn_valid() asserts that there is a memblock entry for a given pfn without
MEMBLOCK_NOMAP flag being set. The problem with ZONE_DEVICE based memory is
that they do not have memblock entries. Hence memblock_is_map_memory() will
invariably fail via memblock_search() for a ZONE_DEVICE based address. This
eventually fails pfn_valid() which is wrong. memblock_is_map_memory() needs
to be skipped for such memory ranges. As ZONE_DEVICE memory gets hotplugged
into the system via memremap_pages() called from a driver, their respective
memory sections will not have SECTION_IS_EARLY set.

Normal hotplug memory will never have MEMBLOCK_NOMAP set in their memblock
regions. Because the flag MEMBLOCK_NOMAP was specifically designed and set
for firmware reserved memory regions. memblock_is_map_memory() can just be
skipped as its always going to be positive and that will be an optimization
for the normal hotplug memory. Like ZONE_DEVICE based memory, all normal
hotplugged memory too will not have SECTION_IS_EARLY set for their sections

Skipping memblock_is_map_memory() for all non early memory sections would
fix pfn_valid() problem for ZONE_DEVICE based memory and also improve its
performance for normal hotplug memory as well.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Acked-by: David Hildenbrand <david@redhat.com>
Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support")
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/1614921898-4099-2-git-send-email-anshuman.khandual@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index b913844ab74040cb737b9c3df37fe86ec0e7efbd..916e0547fdccf7fc5df14b4c885c788edb25a47a 100644 (file)
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -218,6 +218,18 @@ int pfn_valid(unsigned long pfn)
 
        if (!valid_section(__pfn_to_section(pfn)))
                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(__pfn_to_section(pfn)))
+               return pfn_section_valid(__pfn_to_section(pfn), pfn);
 #endif
        return memblock_is_map_memory(addr);
 }