Messages in this thread | | | Date | Thu, 24 Aug 2023 09:50:32 +0200 | From | David Hildenbrand <> | Subject | Re: [PATCH RFC 00/37] Add support for arm64 MTE dynamic tag storage reuse |
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On 23.08.23 15:13, Alexandru Elisei wrote: > Introduction > ============ > > Arm has implemented memory coloring in hardware, and the feature is called > Memory Tagging Extensions (MTE). It works by embedding a 4 bit tag in bits > 59..56 of a pointer, and storing this tag to a reserved memory location. > When the pointer is dereferenced, the hardware compares the tag embedded in > the pointer (logical tag) with the tag stored in memory (allocation tag). > > The relation between memory and where the tag for that memory is stored is > static. > > The memory where the tags are stored have been so far unaccessible to Linux. > This series aims to change that, by adding support for using the tag storage > memory only as data memory; tag storage memory cannot be itself tagged. > > > Implementation > ============== > > The series is based on v6.5-rc3 with these two patches cherry picked: > > - mm: Call arch_swap_restore() from unuse_pte(): > > https://lore.kernel.org/all/20230523004312.1807357-3-pcc@google.com/ > > - arm64: mte: Simplify swap tag restoration logic: > > https://lore.kernel.org/all/20230523004312.1807357-4-pcc@google.com/ > > The above two patches are queued for the v6.6 merge window: > > https://lore.kernel.org/all/20230702123821.04e64ea2c04dd0fdc947bda3@linux-foundation.org/ > > The entire series, including the above patches, can be cloned with: > > $ git clone https://gitlab.arm.com/linux-arm/linux-ae.git \ > -b arm-mte-dynamic-carveout-rfc-v1 > > On the arm64 architecture side, an extension is being worked on that will > clarify how MTE tag storage reuse should behave. The extension will be > made public soon. > > On the Linux side, MTE tag storage reuse is accomplished with the > following changes: > > 1. The tag storage memory is exposed to the memory allocator as a new > migratetype, MIGRATE_METADATA. It behaves similarly to MIGRATE_CMA, with > the restriction that it cannot be used to allocate tagged memory (tag > storage memory cannot be tagged). On tagged page allocation, the > corresponding tag storage is reserved via alloc_contig_range(). > > 2. mprotect(PROT_MTE) is implemented by changing the pte prot to > PAGE_METADATA_NONE. When the page is next accessed, a fault is taken and > the corresponding tag storage is reserved. > > 3. When the code tries to copy tags to a page which doesn't have the tag > storage reserved, the tags are copied to an xarray and restored in > set_pte_at(), when the page is eventually mapped with the tag storage > reserved.
Hi!
after re-reading it 2 times, I still have no clue what your patch set is actually trying to achieve. Probably there is a way to describe how user space intents to interact with this feature, so to see which value this actually has for user space -- and if we are using the right APIs and allocators.
So some dummy questions / statements
1) Is this about re-propusing the memory used to hold tags for different purpose? Or what exactly is user space going to do with the PROT_MTE memory? The whole mprotect(PROT_MTE) approach might not eb the right thing to do.
2) Why do we even have to involve the page allocator if this is some special-purpose memory? Re-porpusing the buddy when later using alloc_contig_range() either way feels wrong.
[...]
> arch/arm64/Kconfig | 13 + > arch/arm64/include/asm/assembler.h | 10 + > arch/arm64/include/asm/memory_metadata.h | 49 ++ > arch/arm64/include/asm/mte-def.h | 16 +- > arch/arm64/include/asm/mte.h | 40 +- > arch/arm64/include/asm/mte_tag_storage.h | 36 ++ > arch/arm64/include/asm/page.h | 5 +- > arch/arm64/include/asm/pgtable-prot.h | 2 + > arch/arm64/include/asm/pgtable.h | 33 +- > arch/arm64/kernel/Makefile | 1 + > arch/arm64/kernel/elfcore.c | 14 +- > arch/arm64/kernel/hibernate.c | 46 +- > arch/arm64/kernel/mte.c | 31 +- > arch/arm64/kernel/mte_tag_storage.c | 667 +++++++++++++++++++++++ > arch/arm64/kernel/setup.c | 7 + > arch/arm64/kvm/arm.c | 6 +- > arch/arm64/lib/mte.S | 30 +- > arch/arm64/mm/copypage.c | 26 + > arch/arm64/mm/fault.c | 35 +- > arch/arm64/mm/mteswap.c | 113 +++- > fs/proc/meminfo.c | 8 + > fs/proc/page.c | 1 + > include/asm-generic/Kbuild | 1 + > include/asm-generic/memory_metadata.h | 50 ++ > include/linux/gfp.h | 10 + > include/linux/gfp_types.h | 14 +- > include/linux/huge_mm.h | 6 + > include/linux/kernel-page-flags.h | 1 + > include/linux/migrate_mode.h | 1 + > include/linux/mm.h | 12 +- > include/linux/mmzone.h | 26 +- > include/linux/page-flags.h | 1 + > include/linux/pgtable.h | 19 + > include/linux/sched.h | 2 +- > include/linux/sched/mm.h | 13 + > include/linux/vm_event_item.h | 5 + > include/linux/vmstat.h | 2 + > include/trace/events/mmflags.h | 5 +- > mm/Kconfig | 5 + > mm/compaction.c | 52 +- > mm/huge_memory.c | 109 ++++ > mm/internal.h | 7 + > mm/khugepaged.c | 7 + > mm/memory.c | 180 +++++- > mm/mempolicy.c | 7 + > mm/migrate.c | 6 + > mm/mm_init.c | 23 +- > mm/mprotect.c | 46 ++ > mm/page_alloc.c | 136 ++++- > mm/page_isolation.c | 19 +- > mm/page_owner.c | 3 +- > mm/shmem.c | 14 +- > mm/show_mem.c | 4 + > mm/swapfile.c | 4 + > mm/vmscan.c | 3 + > mm/vmstat.c | 13 +- > 56 files changed, 1834 insertions(+), 161 deletions(-) > create mode 100644 arch/arm64/include/asm/memory_metadata.h > create mode 100644 arch/arm64/include/asm/mte_tag_storage.h > create mode 100644 arch/arm64/kernel/mte_tag_storage.c > create mode 100644 include/asm-generic/memory_metadata.h
The core-mm changes don't look particularly appealing :)
-- Cheers,
David / dhildenb
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