On 05.03.21 19:13, Catalin Marinas wrote:
On Fri, Mar 05, 2021 at 10:54:57AM +0530, Anshuman Khandual wrote:
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@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support")
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
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);
Would something like this work instead:
if (online_device_section(ms))
return 1;
to avoid the assumptions around early_section()?
Please keep online section logic out of pfn valid logic. Tow different
things. (and rather not diverge too much from generic pfn_valid() - we
want to achieve the opposite in the long term, merging both implementations)
--
Thanks,
David / dhildenb
