On Mon, 21 Oct 2024 at 12:09, Ryan Roberts <ryan.roberts@xxxxxxx> 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. Like in downstream kernels like Fedora/RHEL/etc. I would expect the default would be 4k, but you could override with 16k, 64k, etc. with a karg. > > > > Thanks again and best regards! > > > > (P.S.: Please add the asahi@ mailing list to the CC for future iterations of > > this patch set and tag both Hector and myself in as well. Thanks!) > > Will do! > > > > > > >
