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Tue, 21 May 2024 11:48:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1716292125; bh=w74oySSkmlGhE0TfH1tB7F1tx4YTKjzIh/pSxeIstk8=; h=From:To:Cc:Subject:Date:From; b=Z7Y2msQBI4viLlGJ0SpmMkYpvV3AS1iRehsdy1KRmCwEn7RV12UVquGp0XqkpYfNY v2aE1vjDmYa52XjWBtWrRfspwdE0jHGxK+PwYUvpFLIPi52dq2gHNp4JK79Az0x4Vl c9GvyfNDuZc9fnRcOAc2eza0B26LvqOJEZTA6tqIxXr0IKfjh3gc7Ry63ANlZxfqvE adAQpi119naNEOc24zn/tZAvOm++JqXSUymNnxV96y/k3esg9bWhzOiLbxRcuNBs5e odszu3eEZG+axxtfVKk9WsRbhNSkGYXY5+sARrQLydAe3LcYNsSrAFzJ4ITpn5qcE9 GJUHONG2kQL6Q== From: =?utf-8?b?QmrDtnJuIFTDtnBlbA==?= To: Alexandre Ghiti , Albert Ou , David Hildenbrand , Palmer Dabbelt , Paul Walmsley , linux-riscv@lists.infradead.org, Oscar Salvador Cc: =?utf-8?b?QmrDtnJuIFTDtnBlbA==?= , Andrew Bresticker , Chethan Seshadri , Lorenzo Stoakes , Santosh Mamila , Sivakumar Munnangi , Sunil V L , linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux-foundation.org Subject: [PATCH v3 0/9] riscv: Memory Hot(Un)Plug support Date: Tue, 21 May 2024 13:48:21 +0200 Message-Id: <20240521114830.841660-1-bjorn@kernel.org> X-Mailer: git-send-email 2.40.1 MIME-Version: 1.0 X-Rspam-User: X-Stat-Signature: syz3npzp48wi7edi3qagmz1mnfhahhkr X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E0B2D80002 X-HE-Tag: 1716292130-524513 X-HE-Meta: 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 hpgU6EfU n5fed X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Björn Töpel ================================================================ Memory Hot(Un)Plug support (and ZONE_DEVICE) for the RISC-V port ================================================================ Introduction ============ To quote "Documentation/admin-guide/mm/memory-hotplug.rst": "Memory hot(un)plug allows for increasing and decreasing the size of physical memory available to a machine at runtime." This series adds memory hot(un)plugging, and ZONE_DEVICE support for the RISC-V Linux port. MM configuration ================ RISC-V MM has the following configuration: * Memory blocks are 128M, analogous to x86-64. It uses PMD ("hugepage") vmemmaps. From that follows that 2M (PMD) worth of vmemmap spans 32768 pages á 4K which gets us 128M. * The pageblock size is the minimum minimum virtio_mem size, and on RISC-V it's 2M (2^9 * 4K). Implementation ============== The PGD table on RISC-V is shared/copied between for all processes. To avoid doing page table synchronization, the first patch (patch 1) pre-allocated the PGD entries for vmemmap/direct map. By doing that the init_mm PGD will be fixed at kernel init, and synchronization can be avoided all together. The following two patches (patch 2-3) does some preparations, followed by the actual MHP implementation (patch 4-5). Then, MHP and virtio-mem are enabled (patch 6-7), and finally ZONE_DEVICE support is added (patch 8). MHP and locking =============== TL;DR: The MHP does not step on any toes, except for ptdump. Additional locking is required for ptdump. Long version: For v2 I spent some time digging into init_mm synchronization/update. Here are my findings, and I'd love them to be corrected if incorrect. It's been a gnarly path... The `init_mm` structure is a special mm (perhaps not a "real" one). It's a "lazy context" that tracks kernel page table resources, e.g., the kernel page table (swapper_pg_dir), a kernel page_table_lock (more about the usage below), mmap_lock, and such. `init_mm` does not track/contain any VMAs. Having the `init_mm` is convenient, so that the regular kernel page table walk/modify functions can be used. Now, `init_mm` being special means that the locking for kernel page tables are special as well. On RISC-V the PGD (top-level page table structure), similar to x86, is shared (copied) with user processes. If the kernel PGD is modified, it has to be synched to user-mode processes PGDs. This is avoided by pre-populating the PGD, so it'll be fixed from boot. The in-kernel pgd regions are documented in `Documentation/arch/riscv/vm-layout.rst`. The distinct regions are: * vmemmap * vmalloc/ioremap space * direct mapping of all physical memory * kasan * modules, BPF * kernel Memory hotplug is the process of adding/removing memory to/from the kernel. Adding is done in two phases: 1. Add the memory to the kernel 2. Online memory, making it available to the page allocator. Step 1 is partially architecture dependent, and updates the init_mm page table: * Update the direct map page tables. The direct map is a linear map, representing all physical memory: `virt = phys + PAGE_OFFSET` * Add a `struct page` for each added page of memory. Update the vmemmap (virtual mapping to the `struct page`, so we can easily transform a kernel virtual address to a `struct page *` address. From an MHP perspective, there are two regions of the PGD that are updated: * vmemmap * direct mapping of all physical memory The `struct mm_struct` has a couple of locks in play: * `spinlock_t page_table_lock` protects the page table, and some counters * `struct rw_semaphore mmap_lock` protect an mm's VMAs Note again that `init_mm` does not contain any VMAs, but still uses the mmap_lock in some places. The `page_table_lock` was originally used to to protect all pages tables, but more recently a split page table lock has been introduced. The split lock has a per-table lock for the PTE and PMD tables. If split lock is disabled, all tables are guarded by `mm->page_table_lock` (for user processes). Split page table locks are not used for init_mm. MHP operations is typically synchronized using `DEFINE_STATIC_PERCPU_RWSEM(mem_hotplug_lock)`. Actors ------ The following non-MHP actors in the kernel traverses (read), and/or modifies the kernel PGD. * `ptdump` Walks the entire `init_mm`, via `ptdump_walk_pgd()` with the `mmap_write_lock(init_mm)` taken. Observation: ptdump can race with MHP, and needs additional locking to avoid crashes/races. * `set_direct_*` / `arch/riscv/mm/pageattr.c` The `set_direct_*` functionality is used to "synchronize" the direct map to other kernel mappings, e.g. modules/kernel text. The direct map is using "as large huge table mappings as possible", which means that the `set_direct_*` might need to split the direct map. The `set_direct_*` functions operates with the `mmap_write_lock(init_mm)` taken. Observation: `set_direct_*` uses the direct map, but will never modify the same entry as MHP. If there is a mapping, that entry will never race with MHP. Further, MHP acts when memory is offline. * HVO / `mm/hugetlb_vmemmap` HVO optimizes the backing `struct page` for hugetlb pages, which means changing the "vmemmap" region. HVO can split (merge?) a vmemmap pmd. However, it will never race with MHP, since HVO only operates at online memory. HVO cannot touch memory being MHP added or removed. * `apply_to_page_range` Walks a range, creates pages and applies a callback (setting permissions) for the page. When creating a table, it might use `int __pte_alloc_kernel(pmd_t *pmd)` which takes the `init_mm.page_table_lock` to synchronize pmd populate. Used by: `mm/vmalloc.c` and `mm/kasan/shadow.c`. The KASAN callback takes the `init_mm.page_table_lock` to synchronize pte creation. Observations: `apply_to_page_range` applies to the "vmalloc/ioremap space" region, and "kasan" region. *Not* affected by MHP. * `apply_to_existing_page_range` Walks a range, applies a callback (setting permissions) for the page (no page creation). Used by: `kernel/bpf/arena.c` and `mm/kasan/shadow.c`. The KASAN callback takes the `init_mm.page_table_lock` to synchronize pte creation. *Not* affected by MHP regions. * `apply_to_existing_page_range` applies to the "vmalloc/ioremap space" region, and "kasan" region. *Not* affected by MHP regions. * `ioremap_page_range` and `vmap_page_range` Uses the same internal function, and might create table entries at the "vmalloc/ioremap space" region. Can call `__pte_alloc_kernel()` which takes the `init_mm.page_table_lock` synchronizing pmd populate in the region. *Not* affected by MHP regions. Summary: * MHP add will never modify the same page table entries, as any of the other actors. * MHP remove is done when memory is offlined, and will not clash with any of the actors. * Functions that walk the entire kernel page table need synchronization * It's sufficient to add the MHP lock ptdump. Testing ======= This series adds basic DT supported hotplugging. There is a QEMU series enabling MHP for the RISC-V "virt" machine here: [1] ACPI/MSI support is still in the making for RISC-V, and prior proper (ACPI) PCI MSI support lands [2] and NUMA SRAT support [3], it hard to try it out. I've prepared a QEMU branch with proper ACPI GED/PC-DIMM support [4], and a this series with the required prerequisites [5] (AIA, ACPI AIA MADT, ACPI NUMA SRAT). To test with virtio-mem, e.g.: | qemu-system-riscv64 \ | -machine virt,aia=aplic-imsic \ | -cpu rv64,v=true,vlen=256,elen=64,h=true,zbkb=on,zbkc=on,zbkx=on,zkr=on,zkt=on,svinval=on,svnapot=on,svpbmt=on \ | -nodefaults \ | -nographic -smp 8 -kernel rv64-u-boot.bin \ | -drive file=rootfs.img,format=raw,if=virtio \ | -device virtio-rng-pci \ | -m 16G,slots=3,maxmem=32G \ | -object memory-backend-ram,id=mem0,size=16G \ | -numa node,nodeid=0,memdev=mem0 \ | -serial chardev:char0 \ | -mon chardev=char0,mode=readline \ | -chardev stdio,mux=on,id=char0 \ | -device pci-serial,id=serial0,chardev=char0 \ | -object memory-backend-ram,id=vmem0,size=2G \ | -device virtio-mem-pci,id=vm0,memdev=vmem0,node=0 where "rv64-u-boot.bin" is U-boot with EFI/ACPI-support (use [6] if you're lazy). In the QEMU monitor: | (qemu) info memory-devices | (qemu) qom-set vm0 requested-size 1G ...to test DAX/KMEM, use the follow QEMU parameters: | -object memory-backend-file,id=mem1,share=on,mem-path=virtio_pmem.img,size=4G \ | -device virtio-pmem-pci,memdev=mem1,id=nv1 and the regular ndctl/daxctl dance. If you're brave to try the ACPI branch, add "acpi=on" to "-machine virt", and test PC-DIMM MHP (in addition to virtio-{p},mem): In the QEMU monitor: | (qemu) object_add memory-backend-ram,id=mem1,size=1G | (qemu) device_add pc-dimm,id=dimm1,memdev=mem1 You can also try hot-remove with some QEMU options, say: | -object memory-backend-file,id=mem-1,size=256M,mem-path=/pagesize-2MB | -device pc-dimm,id=mem1,memdev=mem-1 | -object memory-backend-file,id=mem-2,size=1G,mem-path=/pagesize-1GB | -device pc-dimm,id=mem2,memdev=mem-2 | -object memory-backend-file,id=mem-3,size=256M,mem-path=/pagesize-2MB | -device pc-dimm,id=mem3,memdev=mem-3 Remove "acpi=on" to run with DT. Thanks to Alex, Andrew, David, and Oscar for all comments/tests/fixups. Changelog ========= v2->v3: Collect tags 0001-riscv-mm-Properly-forward-vmemmap_populate-altmap * New patch, split from attribute change (Alex, Oscar) 0005-riscv-mm-Add-memory-hotplugging-support * Fix page table free to take PG_reserved into consideration (David, Oscar) * Depend on SPARSE_VMEMMAP (Alex, David, Oscar) * Proper TLB flushing (Alex) 0009-riscv-mm-Add-support-for-ZONE_DEVICE * Fixed 32b build v1->v2: Reviewed a lot of MHP locking scenarios Various config build issues (e.g. build !CONFIG_MEMORY_HOTPLUG) (Andrew) Added arch_get_mappable_range() implementation Acquire MHP lock for ptdump, analogous to arm64 ACPI MHP tests Add ZONE_DEVICE patch References ========== [1] https://lore.kernel.org/qemu-devel/20240521105635.795211-1-bjorn@kernel.org/ [2] https://lore.kernel.org/linux-riscv/20240501121742.1215792-1-sunilvl@ventanamicro.com/ [3] https://lore.kernel.org/linux-riscv/cover.1713778236.git.haibo1.xu@intel.com/ [4] https://github.com/bjoto/qemu/commits/virtio-mem-pc-dimm-mhp-acpi-v2/ [5] https://github.com/bjoto/linux/commits/mhp-v3-next-acpi [6] https://github.com/bjoto/riscv-rootfs-utils/tree/acpi Thanks, Björn Björn Töpel (9): riscv: mm: Properly forward vmemmap_populate() altmap parameter riscv: mm: Pre-allocate vmemmap/direct map PGD entries riscv: mm: Change attribute from __init to __meminit for page functions riscv: mm: Refactor create_linear_mapping_range() for memory hot add riscv: mm: Add memory hotplugging support riscv: mm: Take memory hotplug read-lock during kernel page table dump riscv: Enable memory hotplugging for RISC-V virtio-mem: Enable virtio-mem for RISC-V riscv: mm: Add support for ZONE_DEVICE arch/riscv/Kconfig | 3 + arch/riscv/include/asm/kasan.h | 4 +- arch/riscv/include/asm/mmu.h | 4 +- arch/riscv/include/asm/pgtable-64.h | 20 ++ arch/riscv/include/asm/pgtable-bits.h | 1 + arch/riscv/include/asm/pgtable.h | 19 +- arch/riscv/mm/init.c | 339 +++++++++++++++++++++++--- arch/riscv/mm/ptdump.c | 3 + drivers/virtio/Kconfig | 2 +- 9 files changed, 349 insertions(+), 46 deletions(-) base-commit: 92cce91949a497a8a4615f9ba5813b03f7a1f1d5