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 09:16:42 +0530 |
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On 1/25/21 1:01 PM, Mike Rapoport wrote: > On Mon, Jan 25, 2021 at 11:52:32AM +0530, 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. > > I didn't object to these patches, I think they are fine. > I agree that we can look into update of arm64's pfn_valid(), maybe right > after decrease of section size lands in.
Sure, will drop the RFC tag and prepare these patches.
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