IIRC shoot-downs are one of the reasons for using per-cpu PGDs, which can in-turn enable/underpin other hardening functions... presuming the churn of recent years has softened attitudes toward such core MM changes. https://forum.osdev.org/viewtopic.php?f=15&t=29661 -Boris On Mon, Aug 30, 2021 at 8:02 PM Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> wrote: > > Hi, > > This is a second RFC for the PKS write protected tables concept. I'm sharing to > show the progress to interested people. I'd also appreciate any comments, > especially on the direct map page table protection solution (patch 17). > > Since v1[1], the improvements are: > - Fully handle direct map page tables, and handle hotplug/unplug path. > - Create a debug time checker that scans page tables and verifies > their protection. > - Fix odds-and-ends kernel page tables that showed up with debug > checker. At this point all of the typical normal page tables should be > protected. > - Fix toggling of writablility for odds-and-ends page table modifications found > that don't use the normal helpers. > - Create atomic context grouped page allocator, after finding some page table > allocations that are passing GFP_ATOMIC. > - Create "soft" mode that warns and disables protection on violation instead > of oopsing. > - Boot parameters for disabling pks tables > - Change PageTable set clear to ctor/dtor (peterz) > - Remove VM_BUG_ON_PAGE in alloc_table() (Shakeel Butt) > - PeterZ/Vlastimil had suggested to also build a non-PKS mode for use in > debugging. I skipped it for now because the series was too big. > - Rebased to latest PKS core v7 [2] > > Also, Mike Rapoport has been experimenting[3] with this usage to work on how to > share caches of permissioned/broken pages between use cases. This RFCv2 still > uses the "grouped pages" concept, where each usage would maintain its own > cache, but should be able to integrate with a central solution if something is > developed. > > Next I was planning to look into characterizing/tuning the performance, although > what page allocation scheme is ultimately used will probably impact that. > > This applies on top of the PKS core v7 series[2] and this patch[4]. Testing is > still pretty light. > > This RFC has been acked by Dave Hansen. > > [1] https://lore.kernel.org/lkml/20210505003032.489164-1-rick.p.edgecombe@xxxxxxxxx/ > [2] https://lore.kernel.org/lkml/20210804043231.2655537-1-ira.weiny@xxxxxxxxx/ > [3] https://lore.kernel.org/lkml/20210823132513.15836-1-rppt@xxxxxxxxxx/ > [4] https://lore.kernel.org/lkml/20210818221026.10794-1-rick.p.edgecombe@xxxxxxxxx/ > > Rick Edgecombe (19): > list: Support getting most recent element in list_lru > list: Support list head not in object for list_lru > x86/mm/cpa: Add grouped page allocations > mm: Explicitly zero page table lock ptr > x86, mm: Use cache of page tables > x86/mm/cpa: Add perm callbacks to grouped pages > x86/cpufeatures: Add feature for pks tables > x86/mm/cpa: Add get_grouped_page_atomic() > x86/mm: Support GFP_ATOMIC in alloc_table_node() > x86/mm: Use alloc_table() for fill_pte(), etc > mm/sparsemem: Use alloc_table() for table allocations > x86/mm: Use free_table in unmap path > mm/debug_vm_page_table: Use setters instead of WRITE_ONCE > x86/efi: Toggle table protections when copying > x86/mm/cpa: Add set_memory_pks() > x86/mm: Protect page tables with PKS > x86/mm/cpa: PKS protect direct map page tables > x86/mm: Add PKS table soft mode > x86/mm: Add PKS table debug checking > > .../admin-guide/kernel-parameters.txt | 4 + > arch/x86/boot/compressed/ident_map_64.c | 5 + > arch/x86/include/asm/cpufeatures.h | 2 +- > arch/x86/include/asm/pgalloc.h | 6 +- > arch/x86/include/asm/pgtable.h | 31 +- > arch/x86/include/asm/pgtable_64.h | 33 +- > arch/x86/include/asm/pkeys_common.h | 1 - > arch/x86/include/asm/set_memory.h | 24 + > arch/x86/mm/init.c | 90 +++ > arch/x86/mm/init_64.c | 29 +- > arch/x86/mm/pat/set_memory.c | 527 +++++++++++++++++- > arch/x86/mm/pgtable.c | 183 +++++- > arch/x86/mm/pkeys.c | 4 + > arch/x86/platform/efi/efi_64.c | 8 + > include/asm-generic/pgalloc.h | 46 +- > include/linux/list_lru.h | 26 + > include/linux/mm.h | 16 +- > include/linux/pkeys.h | 1 + > mm/Kconfig | 23 + > mm/debug_vm_pgtable.c | 36 +- > mm/list_lru.c | 38 +- > mm/memory.c | 1 + > mm/sparse-vmemmap.c | 22 +- > mm/swap.c | 6 + > mm/swap_state.c | 5 + > .../arch/x86/include/asm/disabled-features.h | 8 +- > 26 files changed, 1123 insertions(+), 52 deletions(-) > > -- > 2.17.1 > -- Boris Lukashev Systems Architect Semper Victus
