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.mari...@arm.com> >> Cc: Will Deacon <w...@kernel.org> >> Cc: Ard Biesheuvel <a...@kernel.org> >> Cc: Robin Murphy <robin.mur...@arm.com> >> Cc: linux-arm-ker...@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support") >> Signed-off-by: Anshuman Khandual <anshuman.khand...@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?). 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?) -- Thanks, David / dhildenb