| CVD x86 kernel build | Need to rebuild the x86_64 Cuttlefish kernel dist from /home/nzzhao/learn_os/pixel/common_my_dec | Run /home/nzzhao/learn_os/pixel/build_x86_64.sh (default lane my_dec, target //common_my_dec:kernel_x86_64_dist) | out/kernel_x86_64/dist/{bzImage,vmlinux,boot.img,system_dlkm.erofs.img} exist and build_x86_64.sh status records exit_code=0 | Inspect out/kernel_x86_64/logs/build_x86_64-*.log; use build_x86_64.sh stop rather than pkill -f | replace handwritten Bazel command; then follow CVD custom-kernel/DLKM image pairing workflow |
| Preflight | Userspace get_page_size or equivalent is forced to 16KB on a 4KB base-page kernel | Run the search commands in references/userspace-forced-16kb-page-size-audit.md | Raw ART/scudo/bionic/kernel artifacts exist with file:line matches | Broaden search to PAGE_SIZE, gPageSize, mmap, madvise, UFFD, and remap | block runtime conclusion until callsites are classified |
| ART GC | Mark-compact uses partial UFFD registration or MADV_DONTNEED | Inspect KernelPreparation(), UFFD ioctl helpers, and page-status arrays | Ranges are multiples of forced 16KB and therefore kernel-page aligned | Trace UFFDIO_* errno and VMA split/unregister path | branch to UFFD/VMA split analysis |
| Scudo | Secondary allocator remaps or releases cached mappings | Inspect mapSecondary(), MemMapLinux::remapImpl(), and release paths | Remap address/size are 16KB aligned and no MAP_FIXED failure is observed | Capture failing address, size, flags, and neighboring VMAs | branch to fixed-address remap diagnosis |
| Bionic | Small-object allocator maps one allocator page per chunk | Inspect BionicSmallObjectAllocator::alloc_page() and page_start() metadata lookup | page_size(), mmap, munmap, and metadata lookup all use the same forced unit | Check invalid pointer/page signature failures | continue unless metadata lookup is inconsistent |
| VMA Merge | Concern that 16KB alignment changes neighboring VMA merge | Inspect vma_merge predicates and thp_vma_suitable_order() | Merge predicates fail/pass due to flags/file/policy/UFFD/name/anon_vma/pgoff, not userspace page-size alone | Add targeted tracepoint/log for prev/middle/next predicates | replace alignment-only explanation with predicate evidence |
| UFFD order-2 mfill | Restoring or changing the experimental UFFD anonymous order-2 fast path | Default the fast path off, expose a bool core kernel parameter with core_param(uffd_mfill_order2, ..., bool, ...), keep debugfs enabled/stats, and enable B runs with kernel cmdline uffd_mfill_order2=1 | /sys/kernel/debug/uffd_mfill_order2/stats reports enabled 0 for A and enabled 1 plus successes for B | If only debugfs is written after boot, restart the guest because startup ART UFFD events cannot be recovered | branch A/B runs by kernel parameter, not by post-boot mutation |
| COW order-2 mTHP | Changing or measuring the experimental do_wp_page() order-2 COW fast path | Default mthp_cow_order2 off and expose it as a bool core_param; enable only target B/full16K boots with early kernel cmdline mthp_cow_order2=1 | A boots show /sys/module/kernel/parameters/mthp_cow_order2=N; B/full16K boots show cmdline and parameter enabled before app startup; COW vmstat counters move only in enabled cells | If the parameter is written only after boot, treat startup COW attribution as contaminated and reboot with the intended cmdline | branch A/B runs by boot parameter, not by post-boot mutation |
| CVD Kernel Bring-Up | Kernel build prints Kernel ABI header warnings from tools/perf or tools/objtool | Treat as a tools header-sync warning, not Android GKI/KMI enforcement; separately check vendor ramdisk module ABI | tools/perf/check-headers.sh or tools/objtool/sync-check.sh emits the warning, and modinfo vermagic for ramdisk modules matches the booted kernel | If first-stage init reports insmod ... Exec format error, replace/rebuild vendor ramdisk modules for the new kernel | branch away from perf header sync; block only on module ABI/vermagic mismatch |
| CVD x86 mmap Alignment | Pixel arm64 generic_get_unmapped_area() 16KB patch works, but CVD x86_64 OAT BSS runtime address remains 4KB-skewed | Patch arch/x86/kernel/sys_x86_64.c because x86_64 defines HAVE_ARCH_UNMAPPED_AREA; apply the 16KB mask to bottom-up and topdown non-MAP_FIXED paths | arch/x86/kernel/sys_x86_64.c sets info.align_mask for both arch paths, kernel dist rebuilds, and OAT BSS unaligned bss disappears from logcat | If skew remains, inspect ART ELF local_reservation.Begin() and /proc/<pid>/maps for actual reservation base | replace generic-only kernel assumption for CVD x86 |
| CVD Custom Kernel Images | Booting a self-built CVD x86 kernel with changed module ABI | Rebuild first-stage vendor ramdisk modules, replace system_dlkm in super with matching kernel dist system_dlkm.flatten.*.img, and refresh vbmeta_system_dlkm | Kernel log loads /lib/modules/* and /system/lib/modules/* without this_module section size aborts | If /vendor/bin/dlkm_loader aborts on old virtual-device vendor modules, replace vendor_dlkm with matching modules or an empty experimental image plus refreshed vbmeta_vendor_dlkm | block ART validation until dlkm_loader no longer aborts |
| CVD SELinux Noise | Experimental empty or mismatched vendor_dlkm lets ART pass but SystemServer dies on ashmem/device SELinux denials | Relaunch only the validation run with --extra_bootconfig_args='androidboot.selinux=permissive' and clearly mark the result as permissive | logcat shows permissive=1, BOOT_COMPLETED, and no ART OAT/MarkCompact blockers | If boot still fails, treat the new fatal as a separate platform/policy issue, not an ART alignment blocker unless ART markers recur | branch runtime validation while preserving the ART alignment conclusion |
| do_wp_page mTHP COW | Designing or patching write-fault COW to copy an anonymous mTHP/order-2 window | Read references/do-wp-page-mthp-cow-audit-20260710.md, start with FAULT_FLAG_WRITE only, skip UFFD-armed/KSM/zero/special/non-present/pinned/partial-source-folio cases, and keep order-0 wp_page_copy() fallback | File:line audit covers do_wp_page, wp_page_copy, alloc_anon_folio, rmap/GUP/UFFD/KSM and test entry points; candidate patch validates all PTEs under PTL before clear/install | If any gate is not mechanically verifiable, do not batch COW; collect a fallback reason and return to current order-0 path | branch experimental patch behind a knob or tight order-2 gate before broad enablement |
| Pixel common object validation | Temporary gki_defconfig object build fails in scripts/gendwarfksyms with missing host dwarf.h before reaching the target object | For syntax-only local validation, use a temporary O= tree and disable CONFIG_GENDWARFKSYMS, CONFIG_DEBUG_INFO_BTF, and CONFIG_DEBUG_INFO_BTF_MODULES before olddefconfig; keep real release/KMI builds on the proper host dependency set | Target object such as mm/memory.o compiles in the temp tree and the config delta is isolated outside the source tree | If ABI/KMI, BTF, or release validation is required, install the missing DWARF/BTF host dependencies instead of disabling these configs | branch local syntax validation only; do not treat it as a release-build substitute |
