Messages in this thread | | | Date | Mon, 25 Jan 2021 09:31:02 +0200 | From | Mike Rapoport <> | Subject | Re: [RFC 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory |
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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.
> - Anshuman
-- Sincerely yours, Mike.
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