Messages in this thread | | | Subject | Re: [RFC 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory | From | Anshuman Khandual <> | Date | Wed, 27 Jan 2021 09:36:20 +0530 |
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On 1/25/21 2:43 PM, David Hildenbrand wrote: > On 25.01.21 07:22, Anshuman Khandual wrote: >> >> On 12/22/20 12:42 PM, Anshuman Khandual wrote: >>> 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_DEVIE based memory, all hotplugged >>> normal 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 >>> Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support") >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> >> Hello David/Mike, >> >> Given that we would need to rework early sections, memblock semantics via a >> new config i.e EARLY_SECTION_MEMMAP_HOLES and also some possible changes to >> ARCH_KEEP_MEMBLOCK and HAVE_ARCH_PFN_VALID, wondering if these patches here >> which fixes a problem (and improves performance) can be merged first. After >> that, I could start working on the proposed rework. Could you please let me >> know your thoughts on this. Thank you. > > As I said, we might have to throw in an pfn_section_valid() check, to > catch not-section-aligned ZONE_DEVICE ranges (I assume this is possible > on arm64 as well, no?).
pfn_section_valid() should be called only for !early_section() i.e normal hotplug and ZONE_DEVICE memory ? Because early boot memory should always be section aligned.
> > Apart from that, I'm fine with a simple fix upfront, that can be more > easily backported if needed. (Q: do we? is this stable material?) >
Right, an upfront fix here would help in backporting. AFAICS it should be backported to the stable as pte_devmap and ZONE_DEVICE have been around for some time now. Do you have a particular stable version which needs to be tagged in the patch ?
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