From: Anshuman Khandual <anshuman.khandual@arm.com>

Date: Fri, 5 Mar 2021 10:54:57 +0530

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

Git-commit: eeb0753ba27b26f609e61f9950b14f1b934fe429

Patch-mainline: v5.12-rc3

References: git-fixes

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: Mian Yousaf Kaukab <ykaukab@suse.de>

---

 arch/arm64/mm/init.c | 12 ++++++++++++

 1 file changed, 12 insertions(+)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c

index 0ace5e68efba..5920c527845a 100644

--- a/arch/arm64/mm/init.c

+++ b/arch/arm64/mm/init.c

@@ -230,6 +230,18 @@ 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);

 }

-- 

2.26.2