Re: [RFC PATCH v1 00/57] Boot-time page size selection for arm64

[Nick Chan <towinchenmi@gmail.com>]

Neal Gompa 於 2024/10/22 下午5:33 寫道:
> On Mon, Oct 21, 2024 at 11:02 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> On 21/10/2024 14:49, Neal Gompa wrote:
>>> On Mon, Oct 21, 2024 at 7:51 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>>>
>>>> On 21/10/2024 12:32, Eric Curtin wrote:
>>>>> On Mon, 21 Oct 2024 at 12:09, Ryan Roberts <ryan.roberts@arm.com> wrote:
>>>>>>
>>>>>> On 19/10/2024 16:47, Neal Gompa wrote:
>>>>>>> On Monday, October 14, 2024 6:55:11 AM EDT Ryan Roberts wrote:
>>>>>>>> Hi All,
>>>>>>>>
>>>>>>>> Patch bomb incoming... This covers many subsystems, so I've included a core
>>>>>>>> set of people on the full series and additionally included maintainers on
>>>>>>>> relevant patches. I haven't included those maintainers on this cover letter
>>>>>>>> since the numbers were far too big for it to work. But I've included a link
>>>>>>>> to this cover letter on each patch, so they can hopefully find their way
>>>>>>>> here. For follow up submissions I'll break it up by subsystem, but for now
>>>>>>>> thought it was important to show the full picture.
>>>>>>>>
>>>>>>>> This RFC series implements support for boot-time page size selection within
>>>>>>>> the arm64 kernel. arm64 supports 3 base page sizes (4K, 16K, 64K), but to
>>>>>>>> date, page size has been selected at compile-time, meaning the size is
>>>>>>>> baked into a given kernel image. As use of larger-than-4K page sizes become
>>>>>>>> more prevalent this starts to present a problem for distributions.
>>>>>>>> Boot-time page size selection enables the creation of a single kernel
>>>>>>>> image, which can be told which page size to use on the kernel command line.
>>>>>>>>
>>>>>>>> Why is having an image-per-page size problematic?
>>>>>>>> =================================================
>>>>>>>>
>>>>>>>> Many traditional distros are now supporting both 4K and 64K. And this means
>>>>>>>> managing 2 kernel packages, along with drivers for each. For some, it means
>>>>>>>> multiple installer flavours and multiple ISOs. All of this adds up to a
>>>>>>>> less-than-ideal level of complexity. Additionally, Android now supports 4K
>>>>>>>> and 16K kernels. I'm told having to explicitly manage their KABI for each
>>>>>>>> kernel is painful, and the extra flash space required for both kernel
>>>>>>>> images and the duplicated modules has been problematic. Boot-time page size
>>>>>>>> selection solves all of this.
>>>>>>>>
>>>>>>>> Additionally, in starting to think about the longer term deployment story
>>>>>>>> for D128 page tables, which Arm architecture now supports, a lot of the
>>>>>>>> same problems need to be solved, so this work sets us up nicely for that.
>>>>>>>>
>>>>>>>> So what's the down side?
>>>>>>>> ========================
>>>>>>>>
>>>>>>>> Well nothing's free; Various static allocations in the kernel image must be
>>>>>>>> sized for the worst case (largest supported page size), so image size is in
>>>>>>>> line with size of 64K compile-time image. So if you're interested in 4K or
>>>>>>>> 16K, there is a slight increase to the image size. But I expect that
>>>>>>>> problem goes away if you're compressing the image - its just some extra
>>>>>>>> zeros. At boot-time, I expect we could free the unused static storage once
>>>>>>>> we know the page size - although that would be a follow up enhancement.
>>>>>>>>
>>>>>>>> And then there is performance. Since PAGE_SIZE and friends are no longer
>>>>>>>> compile-time constants, we must look up their values and do arithmetic at
>>>>>>>> runtime instead of compile-time. My early perf testing suggests this is
>>>>>>>> inperceptible for real-world workloads, and only has small impact on
>>>>>>>> microbenchmarks - more on this below.
>>>>>>>>
>>>>>>>> Approach
>>>>>>>> ========
>>>>>>>>
>>>>>>>> The basic idea is to rid the source of any assumptions that PAGE_SIZE and
>>>>>>>> friends are compile-time constant, but in a way that allows the compiler to
>>>>>>>> perform the same optimizations as was previously being done if they do turn
>>>>>>>> out to be compile-time constant. Where constants are required, we use
>>>>>>>> limits; PAGE_SIZE_MIN and PAGE_SIZE_MAX. See commit log in patch 1 for full
>>>>>>>> description of all the classes of problems to solve.
>>>>>>>>
>>>>>>>> By default PAGE_SIZE_MIN=PAGE_SIZE_MAX=PAGE_SIZE. But an arch may opt-in to
>>>>>>>> boot-time page size selection by defining PAGE_SIZE_MIN & PAGE_SIZE_MAX.
>>>>>>>> arm64 does this if the user selects the CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
>>>>>>>> Kconfig, which is an alternative to selecting a compile-time page size.
>>>>>>>>
>>>>>>>> When boot-time page size is active, the arch pgtable geometry macro
>>>>>>>> definitions resolve to something that can be configured at boot. The arm64
>>>>>>>> implementation in this series mainly uses global, __ro_after_init
>>>>>>>> variables. I've tried using alternatives patching, but that performs worse
>>>>>>>> than loading from memory; I think due to code size bloat.
>>>>>>>>
>>>>>>>> Status
>>>>>>>> ======
>>>>>>>>
>>>>>>>> When CONFIG_ARM64_BOOT_TIME_PAGE_SIZE is selected, I've only implemented
>>>>>>>> enough to compile the kernel image itself with defconfig (and a few other
>>>>>>>> bits and pieces). This is enough to build a kernel that can boot under QEMU
>>>>>>>> or FVP. I'll happily do the rest of the work to enable all the extra
>>>>>>>> drivers, but wanted to get feedback on the shape of this effort first. If
>>>>>>>> anyone wants to do any testing, and has a must-have config, let me know and
>>>>>>>> I'll prioritize enabling it first.
>>>>>>>>
>>>>>>>> The series is arranged as follows:
>>>>>>>>
>>>>>>>>   - patch 1:    Add macros required for converting non-arch code to support
>>>>>>>>                 boot-time page size selection
>>>>>>>>   - patches 2-36:  Remove PAGE_SIZE compile-time constant assumption from
>>>>>>>> all non-arch code
>>>>>>>>   - patches 37-38: Some arm64 tidy ups
>>>>>>>>   - patch 39:           Add macros required for converting arm64 code to
>>>>>>> support
>>>>>>>>                 boot-time page size selection
>>>>>>>>   - patches 40-56: arm64 changes to support boot-time page size selection
>>>>>>>>   - patch 57:           Add arm64 Kconfig option to enable boot-time page
>>>>>>> size
>>>>>>>>                 selection
>>>>>>>>
>>>>>>>> Ideally, I'd like to get the basics merged (something like this series),
>>>>>>>> then incrementally improve it over a handful of kernel releases until we
>>>>>>>> can demonstrate that we have feature parity with the compile-time build and
>>>>>>>> no performance blockers. Once at that point, ideally the compile-time build
>>>>>>>> options would be removed and the code could be cleaned up further.
>>>>>>>>
>>>>>>>> One of the bigger peices that I'd propose to add as a follow up, is to make
>>>>>>>> va-size boot-time selectable too. That will greatly simplify LPA2 fallback
>>>>>>>> handling.
>>>>>>>>
>>>>>>>> Assuming people are ammenable to the rough shape, how would I go about
>>>>>>>> getting the non-arch changes merged? Since they cover many subsystems, will
>>>>>>>> each piece need to go independently to each relevant maintainer or could it
>>>>>>>> all be merged together through the arm64 tree?
>>>>>>>>
>>>>>>>> Image Size
>>>>>>>> ==========
>>>>>>>>
>>>>>>>> The below shows the size of a defconfig (+ xfs, squashfs, ftrace, kprobes)
>>>>>>>> kernel image on disk for base (before any changes applied), compile (with
>>>>>>>> changes, configured for compile-time page size) and boot (with changes,
>>>>>>>> configured for boot-time page size).
>>>>>>>>
>>>>>>>> You can see the that compile-16k and 64k configs are actually slightly
>>>>>>>> smaller than the baselines; that's due to optimizing some buffer sizes
>>>>>>>> which didn't need to depend on page size during the series. The boot-time
>>>>>>>> image is ~1% bigger than the 64k compile-time image. I believe there is
>>>>>>>> scope to improve this to make it
>>>>>>>> equal to compile-64k if required:
>>>>>>>> | config      | size/KB | diff/KB |  diff/% |
>>>>>>>> |
>>>>>>>> |-------------|---------|---------|---------|
>>>>>>>> |
>>>>>>>> | base-4k     |   54895 |       0 |    0.0% |
>>>>>>>> | base-16k    |   55161 |     266 |    0.5% |
>>>>>>>> | base-64k    |   56775 |    1880 |    3.4% |
>>>>>>>> | compile-4k  |   54895 |       0 |    0.0% |
>>>>>>>> | compile-16k |   55097 |     202 |    0.4% |
>>>>>>>> | compile-64k |   56391 |    1496 |    2.7% |
>>>>>>>> | boot-4K     |   57045 |    2150 |    3.9% |
>>>>>>>>
>>>>>>>> And below shows the size of the image in memory at run-time, separated for
>>>>>>>> text and data costs. The boot image has ~1% text cost; most likely due to
>>>>>>>> the fact that PAGE_SIZE and friends are not compile-time constants so need
>>>>>>>> instructions to load the values and do arithmetic. I believe we could
>>>>>>>> eventually get the data cost to match the cost for the compile image for
>>>>>>>> the chosen page size by freeing
>>>>>>>> the ends of the static buffers not needed for the selected page size:
>>>>>>>> |             |    text |    text |    text |    data |    data |    data |
>>>>>>>> |
>>>>>>>> | config      | size/KB | diff/KB |  diff/% | size/KB | diff/KB |  diff/% |
>>>>>>>> |
>>>>>>>> |-------------|---------|---------|---------|---------|---------|---------|
>>>>>>>> |
>>>>>>>> | base-4k     |   20561 |       0 |    0.0% |   14314 |       0 |    0.0% |
>>>>>>>> | base-16k    |   20439 |    -122 |   -0.6% |   14625 |     311 |    2.2% |
>>>>>>>> | base-64k    |   20435 |    -126 |   -0.6% |   15673 |    1359 |    9.5% |
>>>>>>>> | compile-4k  |   20565 |       4 |    0.0% |   14315 |       1 |    0.0% |
>>>>>>>> | compile-16k |   20443 |    -118 |   -0.6% |   14517 |     204 |    1.4% |
>>>>>>>> | compile-64k |   20439 |    -122 |   -0.6% |   15134 |     820 |    5.7% |
>>>>>>>> | boot-4K     |   20811 |     250 |    1.2% |   15287 |     973 |    6.8% |
>>>>>>>>
>>>>>>>> Functional Testing
>>>>>>>> ==================
>>>>>>>>
>>>>>>>> I've build-tested defconfig for all arches supported by tuxmake (which is
>>>>>>>> most) without issue.
>>>>>>>>
>>>>>>>> I've boot-tested arm64 with CONFIG_ARM64_BOOT_TIME_PAGE_SIZE for all page
>>>>>>>> sizes and a few va-sizes, and additionally have run all the mm-selftests,
>>>>>>>> with no regressions observed vs the equivalent compile-time page size build
>>>>>>>> (although the mm-selftests have a few existing failures when run against
>>>>>>>> 16K and 64K kernels - those should really be investigated and fixed
>>>>>>>> independently).
>>>>>>>>
>>>>>>>> Test coverage is lacking for many of the drivers that I've touched, but in
>>>>>>>> many cases, I'm hoping the changes are simple enough that review might
>>>>>>>> suffice?
>>>>>>>>
>>>>>>>> Performance Testing
>>>>>>>> ===================
>>>>>>>>
>>>>>>>> I've run some limited performance benchmarks:
>>>>>>>>
>>>>>>>> First, a real-world benchmark that causes a lot of page table manipulation
>>>>>>>> (and therefore we would expect to see regression here if we are going to
>>>>>>>> see it anywhere); kernel compilation. It barely registers a change. Values
>>>>>>>> are times,
>>>>>>>> so smaller is better. All relative to base-4k:
>>>>>>>> |             |    kern |    kern |    user |    user |    real |    real |
>>>>>>>> |
>>>>>>>> | config      |    mean |   stdev |    mean |   stdev |    mean |   stdev |
>>>>>>>> |
>>>>>>>> |-------------|---------|---------|---------|---------|---------|---------|
>>>>>>>> |
>>>>>>>> | base-4k     |    0.0% |    1.1% |    0.0% |    0.3% |    0.0% |    0.3% |
>>>>>>>> | compile-4k  |   -0.2% |    1.1% |   -0.2% |    0.3% |   -0.1% |    0.3% |
>>>>>>>> | boot-4k     |    0.1% |    1.0% |   -0.3% |    0.2% |   -0.2% |    0.2% |
>>>>>>>>
>>>>>>>> The Speedometer JavaScript benchmark also shows no change. Values are runs
>>>>>>>> per
>>>>>>>> min, so bigger is better. All relative to base-4k:
>>>>>>>> | config      |    mean |   stdev |
>>>>>>>> |
>>>>>>>> |-------------|---------|---------|
>>>>>>>> |
>>>>>>>> | base-4k     |    0.0% |    0.8% |
>>>>>>>> | compile-4k  |    0.4% |    0.8% |
>>>>>>>> | boot-4k     |    0.0% |    0.9% |
>>>>>>>>
>>>>>>>> Finally, I've run some microbenchmarks known to stress page table
>>>>>>>> manipulations (originally from David Hildenbrand). The fork test
>>>>>>>> maps/allocs 1G of anon memory, then measures the cost of fork(). The munmap
>>>>>>>> test maps/allocs 1G of anon memory then measures the cost of munmap()ing
>>>>>>>> it. The fork test is known to be extremely sensitive to any changes that
>>>>>>>> cause instructions to be aligned differently in cachelines. When using this
>>>>>>>> test for other changes, I've seen double digit regressions for the
>>>>>>>> slightest thing, so 12% regression on this test is actually fairly good.
>>>>>>>> This likely represents the extreme worst case for regressions that will be
>>>>>>>> observed across other microbenchmarks (famous last
>>>>>>>> words). Values are times, so smaller is better. All relative to base-4k:
>>>>>>>> |             |    fork |    fork |  munmap |  munmap |
>>>>>>>> |
>>>>>>>> | config      |    mean |   stdev |   stdev |   stdev |
>>>>>>>> |
>>>>>>>> |-------------|---------|---------|---------|---------|
>>>>>>>> |
>>>>>>>> | base-4k     |    0.0% |    1.3% |    0.0% |    0.3% |
>>>>>>>> | compile-4k  |    0.1% |    1.3% |   -0.9% |    0.1% |
>>>>>>>> | boot-4k     |   12.8% |    1.2% |    3.8% |    1.0% |
>>>>>>>>
>>>>>>>> NOTE: The series applies on top of v6.11.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Ryan
>>>>>>>>
>>>>>>>>
>>>>>>>> Ryan Roberts (57):
>>>>>>>>   mm: Add macros ahead of supporting boot-time page size selection
>>>>>>>>   vmlinux: Align to PAGE_SIZE_MAX
>>>>>>>>   mm/memcontrol: Fix seq_buf size to save memory when PAGE_SIZE is large
>>>>>>>>   mm/page_alloc: Make page_frag_cache boot-time page size compatible
>>>>>>>>   mm: Avoid split pmd ptl if pmd level is run-time folded
>>>>>>>>   mm: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   fs: Introduce MAX_BUF_PER_PAGE_SIZE_MAX for array sizing
>>>>>>>>   fs: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   fs/nfs: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   fs/ext4: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   fork: Permit boot-time THREAD_SIZE determination
>>>>>>>>   cgroup: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   bpf: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   pm/hibernate: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   stackdepot: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   perf: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   kvm: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   trace: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   crash: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   crypto: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   sunrpc: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   sound: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   net: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   net: fec: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   net: marvell: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   net: hns3: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   net: e1000: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   net: igbvf: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   net: igb: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   drivers/base: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   edac: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   optee: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   random: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   sata_sil24: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   virtio: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   xen: Remove PAGE_SIZE compile-time constant assumption
>>>>>>>>   arm64: Fix macros to work in C code in addition to the linker script
>>>>>>>>   arm64: Track early pgtable allocation limit
>>>>>>>>   arm64: Introduce macros required for boot-time page selection
>>>>>>>>   arm64: Refactor early pgtable size calculation macros
>>>>>>>>   arm64: Pass desired page size on command line
>>>>>>>>   arm64: Divorce early init from PAGE_SIZE
>>>>>>>>   arm64: Clean up simple cases of CONFIG_ARM64_*K_PAGES
>>>>>>>>   arm64: Align sections to PAGE_SIZE_MAX
>>>>>>>>   arm64: Rework trampoline rodata mapping
>>>>>>>>   arm64: Generalize fixmap for boot-time page size
>>>>>>>>   arm64: Statically allocate and align for worst-case page size
>>>>>>>>   arm64: Convert switch to if for non-const comparison values
>>>>>>>>   arm64: Convert BUILD_BUG_ON to VM_BUG_ON
>>>>>>>>   arm64: Remove PAGE_SZ asm-offset
>>>>>>>>   arm64: Introduce cpu features for page sizes
>>>>>>>>   arm64: Remove PAGE_SIZE from assembly code
>>>>>>>>   arm64: Runtime-fold pmd level
>>>>>>>>   arm64: Support runtime folding in idmap_kpti_install_ng_mappings
>>>>>>>>   arm64: TRAMP_VALIAS is no longer compile-time constant
>>>>>>>>   arm64: Determine THREAD_SIZE at boot-time
>>>>>>>>   arm64: Enable boot-time page size selection
>>>>>>>>
>>>>>>>>  arch/alpha/include/asm/page.h                 |   1 +
>>>>>>>>  arch/arc/include/asm/page.h                   |   1 +
>>>>>>>>  arch/arm/include/asm/page.h                   |   1 +
>>>>>>>>  arch/arm64/Kconfig                            |  26 ++-
>>>>>>>>  arch/arm64/include/asm/assembler.h            |  78 ++++++-
>>>>>>>>  arch/arm64/include/asm/cpufeature.h           |  44 +++-
>>>>>>>>  arch/arm64/include/asm/efi.h                  |   2 +-
>>>>>>>>  arch/arm64/include/asm/fixmap.h               |  28 ++-
>>>>>>>>  arch/arm64/include/asm/kernel-pgtable.h       | 150 +++++++++----
>>>>>>>>  arch/arm64/include/asm/kvm_arm.h              |  21 +-
>>>>>>>>  arch/arm64/include/asm/kvm_hyp.h              |  11 +
>>>>>>>>  arch/arm64/include/asm/kvm_pgtable.h          |   6 +-
>>>>>>>>  arch/arm64/include/asm/memory.h               |  62 ++++--
>>>>>>>>  arch/arm64/include/asm/page-def.h             |   3 +-
>>>>>>>>  arch/arm64/include/asm/pgalloc.h              |  16 +-
>>>>>>>>  arch/arm64/include/asm/pgtable-geometry.h     |  46 ++++
>>>>>>>>  arch/arm64/include/asm/pgtable-hwdef.h        |  28 ++-
>>>>>>>>  arch/arm64/include/asm/pgtable-prot.h         |   2 +-
>>>>>>>>  arch/arm64/include/asm/pgtable.h              | 133 +++++++++---
>>>>>>>>  arch/arm64/include/asm/processor.h            |  10 +-
>>>>>>>>  arch/arm64/include/asm/sections.h             |   1 +
>>>>>>>>  arch/arm64/include/asm/smp.h                  |   1 +
>>>>>>>>  arch/arm64/include/asm/sparsemem.h            |  15 +-
>>>>>>>>  arch/arm64/include/asm/sysreg.h               |  54 +++--
>>>>>>>>  arch/arm64/include/asm/tlb.h                  |   3 +
>>>>>>>>  arch/arm64/kernel/asm-offsets.c               |   4 +-
>>>>>>>>  arch/arm64/kernel/cpufeature.c                |  93 ++++++--
>>>>>>>>  arch/arm64/kernel/efi.c                       |   2 +-
>>>>>>>>  arch/arm64/kernel/entry.S                     |  60 +++++-
>>>>>>>>  arch/arm64/kernel/head.S                      |  46 +++-
>>>>>>>>  arch/arm64/kernel/hibernate-asm.S             |   6 +-
>>>>>>>>  arch/arm64/kernel/image-vars.h                |  14 ++
>>>>>>>>  arch/arm64/kernel/image.h                     |   4 +
>>>>>>>>  arch/arm64/kernel/pi/idreg-override.c         |  68 +++++-
>>>>>>>>  arch/arm64/kernel/pi/map_kernel.c             | 165 ++++++++++----
>>>>>>>>  arch/arm64/kernel/pi/map_range.c              | 201 ++++++++++++++++--
>>>>>>>>  arch/arm64/kernel/pi/pi.h                     |  63 +++++-
>>>>>>>>  arch/arm64/kernel/relocate_kernel.S           |  10 +-
>>>>>>>>  arch/arm64/kernel/vdso-wrap.S                 |   4 +-
>>>>>>>>  arch/arm64/kernel/vdso.c                      |   7 +-
>>>>>>>>  arch/arm64/kernel/vdso/vdso.lds.S             |   4 +-
>>>>>>>>  arch/arm64/kernel/vdso32-wrap.S               |   4 +-
>>>>>>>>  arch/arm64/kernel/vdso32/vdso.lds.S           |   4 +-
>>>>>>>>  arch/arm64/kernel/vmlinux.lds.S               |  48 +++--
>>>>>>>>  arch/arm64/kvm/arm.c                          |  10 +
>>>>>>>>  arch/arm64/kvm/hyp/nvhe/Makefile              |   1 +
>>>>>>>>  arch/arm64/kvm/hyp/nvhe/host.S                |  10 +-
>>>>>>>>  arch/arm64/kvm/hyp/nvhe/hyp.lds.S             |   4 +-
>>>>>>>>  arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c    |  16 ++
>>>>>>>>  arch/arm64/kvm/mmu.c                          |  39 ++--
>>>>>>>>  arch/arm64/lib/clear_page.S                   |   7 +-
>>>>>>>>  arch/arm64/lib/copy_page.S                    |  33 ++-
>>>>>>>>  arch/arm64/lib/mte.S                          |  27 ++-
>>>>>>>>  arch/arm64/mm/Makefile                        |   1 +
>>>>>>>>  arch/arm64/mm/fixmap.c                        |  38 ++--
>>>>>>>>  arch/arm64/mm/hugetlbpage.c                   |  40 +---
>>>>>>>>  arch/arm64/mm/init.c                          |  26 +--
>>>>>>>>  arch/arm64/mm/kasan_init.c                    |   8 +-
>>>>>>>>  arch/arm64/mm/mmu.c                           |  53 +++--
>>>>>>>>  arch/arm64/mm/pgd.c                           |  12 +-
>>>>>>>>  arch/arm64/mm/pgtable-geometry.c              |  24 +++
>>>>>>>>  arch/arm64/mm/proc.S                          | 128 ++++++++---
>>>>>>>>  arch/arm64/mm/ptdump.c                        |   3 +-
>>>>>>>>  arch/arm64/tools/cpucaps                      |   3 +
>>>>>>>>  arch/csky/include/asm/page.h                  |   3 +
>>>>>>>>  arch/hexagon/include/asm/page.h               |   2 +
>>>>>>>>  arch/loongarch/include/asm/page.h             |   2 +
>>>>>>>>  arch/m68k/include/asm/page.h                  |   1 +
>>>>>>>>  arch/microblaze/include/asm/page.h            |   1 +
>>>>>>>>  arch/mips/include/asm/page.h                  |   1 +
>>>>>>>>  arch/nios2/include/asm/page.h                 |   2 +
>>>>>>>>  arch/openrisc/include/asm/page.h              |   1 +
>>>>>>>>  arch/parisc/include/asm/page.h                |   1 +
>>>>>>>>  arch/powerpc/include/asm/page.h               |   2 +
>>>>>>>>  arch/riscv/include/asm/page.h                 |   1 +
>>>>>>>>  arch/s390/include/asm/page.h                  |   1 +
>>>>>>>>  arch/sh/include/asm/page.h                    |   1 +
>>>>>>>>  arch/sparc/include/asm/page.h                 |   3 +
>>>>>>>>  arch/um/include/asm/page.h                    |   2 +
>>>>>>>>  arch/x86/include/asm/page_types.h             |   2 +
>>>>>>>>  arch/xtensa/include/asm/page.h                |   1 +
>>>>>>>>  crypto/lskcipher.c                            |   4 +-
>>>>>>>>  drivers/ata/sata_sil24.c                      |  46 ++--
>>>>>>>>  drivers/base/node.c                           |   6 +-
>>>>>>>>  drivers/base/topology.c                       |  32 +--
>>>>>>>>  drivers/block/virtio_blk.c                    |   2 +-
>>>>>>>>  drivers/char/random.c                         |   4 +-
>>>>>>>>  drivers/edac/edac_mc.h                        |  13 +-
>>>>>>>>  drivers/firmware/efi/libstub/arm64.c          |   3 +-
>>>>>>>>  drivers/irqchip/irq-gic-v3-its.c              |   2 +-
>>>>>>>>  drivers/mtd/mtdswap.c                         |   4 +-
>>>>>>>>  drivers/net/ethernet/freescale/fec.h          |   3 +-
>>>>>>>>  drivers/net/ethernet/freescale/fec_main.c     |   5 +-
>>>>>>>>  .../net/ethernet/hisilicon/hns3/hns3_enet.h   |   4 +-
>>>>>>>>  drivers/net/ethernet/intel/e1000/e1000_main.c |   6 +-
>>>>>>>>  drivers/net/ethernet/intel/igb/igb.h          |  25 +--
>>>>>>>>  drivers/net/ethernet/intel/igb/igb_main.c     | 149 +++++++------
>>>>>>>>  drivers/net/ethernet/intel/igbvf/netdev.c     |   6 +-
>>>>>>>>  drivers/net/ethernet/marvell/mvneta.c         |   9 +-
>>>>>>>>  drivers/net/ethernet/marvell/sky2.h           |   2 +-
>>>>>>>>  drivers/tee/optee/call.c                      |   7 +-
>>>>>>>>  drivers/tee/optee/smc_abi.c                   |   2 +-
>>>>>>>>  drivers/virtio/virtio_balloon.c               |  10 +-
>>>>>>>>  drivers/xen/balloon.c                         |  11 +-
>>>>>>>>  drivers/xen/biomerge.c                        |  12 +-
>>>>>>>>  drivers/xen/privcmd.c                         |   2 +-
>>>>>>>>  drivers/xen/xenbus/xenbus_client.c            |   5 +-
>>>>>>>>  drivers/xen/xlate_mmu.c                       |   6 +-
>>>>>>>>  fs/binfmt_elf.c                               |  11 +-
>>>>>>>>  fs/buffer.c                                   |   2 +-
>>>>>>>>  fs/coredump.c                                 |   8 +-
>>>>>>>>  fs/ext4/ext4.h                                |  36 ++--
>>>>>>>>  fs/ext4/move_extent.c                         |   2 +-
>>>>>>>>  fs/ext4/readpage.c                            |   2 +-
>>>>>>>>  fs/fat/dir.c                                  |   4 +-
>>>>>>>>  fs/fat/fatent.c                               |   4 +-
>>>>>>>>  fs/nfs/nfs42proc.c                            |   2 +-
>>>>>>>>  fs/nfs/nfs42xattr.c                           |   2 +-
>>>>>>>>  fs/nfs/nfs4proc.c                             |   2 +-
>>>>>>>>  include/asm-generic/pgtable-geometry.h        |  71 +++++++
>>>>>>>>  include/asm-generic/vmlinux.lds.h             |  38 ++--
>>>>>>>>  include/linux/buffer_head.h                   |   1 +
>>>>>>>>  include/linux/cpumask.h                       |   5 +
>>>>>>>>  include/linux/linkage.h                       |   4 +-
>>>>>>>>  include/linux/mm.h                            |  17 +-
>>>>>>>>  include/linux/mm_types.h                      |  15 +-
>>>>>>>>  include/linux/mm_types_task.h                 |   2 +-
>>>>>>>>  include/linux/mmzone.h                        |   3 +-
>>>>>>>>  include/linux/netlink.h                       |   6 +-
>>>>>>>>  include/linux/percpu-defs.h                   |   4 +-
>>>>>>>>  include/linux/perf_event.h                    |   2 +-
>>>>>>>>  include/linux/sched.h                         |   4 +-
>>>>>>>>  include/linux/slab.h                          |   7 +-
>>>>>>>>  include/linux/stackdepot.h                    |   6 +-
>>>>>>>>  include/linux/sunrpc/svc.h                    |   8 +-
>>>>>>>>  include/linux/sunrpc/svc_rdma.h               |   4 +-
>>>>>>>>  include/linux/sunrpc/svcsock.h                |   2 +-
>>>>>>>>  include/linux/swap.h                          |  17 +-
>>>>>>>>  include/linux/swapops.h                       |   6 +-
>>>>>>>>  include/linux/thread_info.h                   |  10 +-
>>>>>>>>  include/xen/page.h                            |   2 +
>>>>>>>>  init/main.c                                   |   7 +-
>>>>>>>>  kernel/bpf/core.c                             |   9 +-
>>>>>>>>  kernel/bpf/ringbuf.c                          |  54 ++---
>>>>>>>>  kernel/cgroup/cgroup.c                        |   8 +-
>>>>>>>>  kernel/crash_core.c                           |   2 +-
>>>>>>>>  kernel/events/core.c                          |   2 +-
>>>>>>>>  kernel/fork.c                                 |  71 +++----
>>>>>>>>  kernel/power/power.h                          |   2 +-
>>>>>>>>  kernel/power/snapshot.c                       |   2 +-
>>>>>>>>  kernel/power/swap.c                           | 129 +++++++++--
>>>>>>>>  kernel/trace/fgraph.c                         |   2 +-
>>>>>>>>  kernel/trace/trace.c                          |   2 +-
>>>>>>>>  lib/stackdepot.c                              |   6 +-
>>>>>>>>  mm/kasan/report.c                             |   3 +-
>>>>>>>>  mm/memcontrol.c                               |  11 +-
>>>>>>>>  mm/memory.c                                   |   4 +-
>>>>>>>>  mm/mmap.c                                     |   2 +-
>>>>>>>>  mm/page-writeback.c                           |   2 +-
>>>>>>>>  mm/page_alloc.c                               |  31 +--
>>>>>>>>  mm/slub.c                                     |   2 +-
>>>>>>>>  mm/sparse.c                                   |   2 +-
>>>>>>>>  mm/swapfile.c                                 |   2 +-
>>>>>>>>  mm/vmalloc.c                                  |   7 +-
>>>>>>>>  net/9p/trans_virtio.c                         |   4 +-
>>>>>>>>  net/core/hotdata.c                            |   4 +-
>>>>>>>>  net/core/skbuff.c                             |   4 +-
>>>>>>>>  net/core/sysctl_net_core.c                    |   2 +-
>>>>>>>>  net/sunrpc/cache.c                            |   3 +-
>>>>>>>>  net/unix/af_unix.c                            |   2 +-
>>>>>>>>  sound/soc/soc-utils.c                         |   4 +-
>>>>>>>>  virt/kvm/kvm_main.c                           |   2 +-
>>>>>>>>  172 files changed, 2185 insertions(+), 951 deletions(-)
>>>>>>>>  create mode 100644 arch/arm64/include/asm/pgtable-geometry.h
>>>>>>>>  create mode 100644 arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c
>>>>>>>>  create mode 100644 arch/arm64/mm/pgtable-geometry.c
>>>>>>>>  create mode 100644 include/asm-generic/pgtable-geometry.h
>>>>>>>>
>>>>>>>> --
>>>>>>>> 2.43.0
>>>>>>>
>>>>>>> This is a generally very exciting patch set! I'm looking forward to seeing it
>>>>>>> land so I can take advantage of it for Fedora ARM and Fedora Asahi Remix.
>>>>>>>
>>>>>>> That said, I have a couple of questions:
>>>>>>>
>>>>>>> * Going forward, how would we handle drivers/modules that require a particular
>>>>>>> page size? For example, the Apple Silicon IOMMU driver code requires the
>>>>>>> kernel to operate in 16k page size mode, and it would need to be disabled in
>>>>>>> other page sizes.
>>>>>>
>>>>>> I think these drivers would want to check PAGE_SIZE at probe time and fail if an
>>>>>> unsupported page size is in use. Do you see any issue with that?
>>>>>>
>>>>>>>
>>>>>>> * How would we handle an invalid selection at boot?
>>>>>>
>>>>>> What do you mean by invalid here? The current policy validates that the
>>>>>> requested page size is supported by the HW by checking mmfr0. If no page size is
>>>>>> passed on the command line, or the passed value is not supported by the HW, then
>>>>>> the we default to the largest page size supported by the HW (so for Apple
>>>>>> Silicon that would be 16k since the HW doesn't support 64k). Although I think it
>>>>>> may be better to change that policy to use the smallest page size in this case;
>>>>>> 4k is the safer bet for compat and will waste much less memory than 64k.
>>>>>>
>>>>>>> Can we program in a
>>>>>>> fallback when the "wrong" mode is selected for a chip or something similar?
>>>>>>
>>>>>> Do you mean effectively add a machanism to force 16k if the detected HW is Apple
>>>>>> Silicon? The trouble is that we need to select the page size, very early in
>>>>>> boot, before start_kernel() is called, so we really only have generic arch code
>>>>>> and the command line with which to make the decision.
>>>>>
>>>>> Yes... I think a build-time CONFIG for default page size, which can be
>>>>> overridden by a karg makes sense... Even on platforms like Apple
>>>>> Silicon you may want to test very specific things in 4k by overriding
>>>>> with a karg.
>>>>
>>>> Ahh, yes, that would certainly work. I'll work it into the next version.
>>>>
>>>
>>> Could we maybe extend to have some kind of way to include a table of
>>> SoC IDs that certain modes are disabled (e.g. 64k on Apple Silicon)
>>
>> 64k is already disabled on Apple Silicon because mmfr0 reports that 64k is not
>> supported.
>>
>>> and preferred modes when no arg is set (16k for Apple Silicon)? That
>>
>> And it's not obvious that we should hard-code a page size preference to a SoC
>> ID. If the CPU can support multiple page sizes, it should be up to the SW stack
>> to decide, not the SoC.
>>
>> I'm guessing your desire is to have a single kernel build that will boot 16k by
>> default on Apple Silicon and 4k by default on other systems, all without needing
>> to modify the command line? Personally I think it's cleaner to just require
>> setting the page size on the command line in these cases.
>>
>>> way it'd work something like this:
>>>
>>> 1. Table identification of 4/16/64 depending on identified SoC
>> So I'd prefer not to have this
>>
>>> 2. Unidentified ones follow build-time default
>>> 3. karg forces a mode regardless
>> But keep these 2.
>>
> 
Since we are talking about Apple Silicon and page size, I would like to
add that on the Apple Silicon SoCs I am working on, the situation is like
this:

Apple A7 (s5l8960x), A8 (T7000), A8X (T7001): CPU MMU support 4K and 64K
page sizes.

Apple A9 (s8000/s8003), A9X (s8001), A10 (t8010), A10X (t8011), A11 (t8015):
CPU MMU Support 16K and 64K page sizes.

However, all of them have 4K page DART IOMMUs.

> I think it makes sense to have it, because it's not just Apple Silicon
> where such a preference/requirement may be necessary. Apple Silicon
> technically works at 4k, but is completely broken at 4k because Linux
> cannot do 16k IOMMU with 4k everything else, so being able to at least
> prefer 16k out of the box is important. And SoCs like the NVIDIA Grace
> Hopper platform prefer 64k over other options (though I am unaware of
> a gross incompatibility that effectively requires it like Apple
> Silicon has).
> 
> When we're trying to get to "single generic image that works
> everywhere", stuff like this matters and I would really like you to
> consider it from the lens of "we want things to work as automagic as
> they do on x86".
For me, in order to get to this level of automagic, there do need to be
a table of which SoC should use which page size table.

> 
> 

Nick Chan