On 04/03/2019 11:02 PM, Logan Gunthorpe wrote: > > > On 2019-04-02 10:30 p.m., Anshuman Khandual wrote: >> Memory removal from an arch perspective involves tearing down two different >> kernel based mappings i.e vmemmap and linear while releasing related page >> table pages allocated for the physical memory range to be removed. >> >> Define a common kernel page table tear down helper remove_pagetable() which >> can be used to unmap given kernel virtual address range. In effect it can >> tear down both vmemap or kernel linear mappings. This new helper is called >> from both vmemamp_free() and ___remove_pgd_mapping() during memory removal. >> The argument 'direct' here identifies kernel linear mappings. >> >> Vmemmap mappings page table pages are allocated through sparse mem helper >> functions like vmemmap_alloc_block() which does not cycle the pages through >> pgtable_page_ctor() constructs. Hence while removing it skips corresponding >> destructor construct pgtable_page_dtor(). >> >> While here update arch_add_mempory() to handle __add_pages() failures by >> just unmapping recently added kernel linear mapping. Now enable memory hot >> remove on arm64 platforms by default with ARCH_ENABLE_MEMORY_HOTREMOVE. >> >> This implementation is overall inspired from kernel page table tear down >> procedure on X86 architecture. > > I've been working on very similar things for RISC-V. In fact, I'm > currently in progress on a very similar stripped down version of > remove_pagetable(). (Though I'm fairly certain I've done a bunch of > stuff wrong.) > > Would it be possible to move this work into common code that can be used > by all arches? Seems like, to start, we should be able to support both > arm64 and RISC-V... and maybe even x86 too. > > I'd be happy to help integrate and test such functions in RISC-V. Sure that will be great. The only impediment is pgtable_page_ctor() for kernel linear mapping. This series is based on current arm64 where linear mapping pgtable pages go through pgtable_page_ctor() init sequence but that might be changing soon. If RISC-V does not have pgtable_page_ctor() init for linear mapping and no other arch specific stuff later on we can try to consolidate remove_pagetable() atleast for both the architectures. Then I wondering whether I can transition pud|pmd_large() to pud|pmd_sect().
