Re: [RFC 0/9] Linear Address Masking enabling

[Dmitry Vyukov]

On Fri, Feb 5, 2021 at 4:16 PM Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> Linear Address Masking[1] (LAM) modifies the checking that is applied to
> 64-bit linear addresses, allowing software to use of the untranslated
> address bits for metadata.
>
> The patchset brings support for LAM for userspace addresses.
>
> The most sensitive part of enabling is change in tlb.c, where CR3 flags
> get set. Please take a look that what I'm doing makes sense.
>
> The patchset is RFC quality and the code requires more testing before it
> can be applied.
>
> The userspace API is not finalized yet. The patchset extends API used by
> ARM64: PR_GET/SET_TAGGED_ADDR_CTRL. The API is adjusted to not imply ARM
> TBI: it now allows to request a number of bits of metadata needed and
> report where these bits are located in the address.
>
> There's an alternative proposal[2] for the API based on Intel CET
> interface. Please let us know if you prefer one over another.
>
> The feature competes for bits with 5-level paging: LAM_U48 makes it
> impossible to map anything about 47-bits. The patchset made these
> capability mutually exclusive: whatever used first wins. LAM_U57 can be
> combined with mappings above 47-bits.
>
> I include QEMU patch in case if somebody wants to play with the feature.

Exciting! Do you plan to send the QEMU patch to QEMU?

> The branch:
>
>         git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git lam
>
> Any comments are welcome.
>
> [1] ISE, Chapter 14. https://software.intel.com/content/dam/develop/external/us/en/documents-tps/architecture-instruction-set-extensions-programming-reference.pdf
> [2] https://github.com/hjl-tools/linux/commit/e85fa032e5b276ddf17edd056f92f599db9e8369
>
> Kirill A. Shutemov (9):
>   mm, arm64: Update PR_SET/GET_TAGGED_ADDR_CTRL interface
>   x86/mm: Fix CR3_ADDR_MASK
>   x86: CPUID and CR3/CR4 flags for Linear Address Masking
>   x86/mm: Introduce TIF_LAM_U57 and TIF_LAM_U48
>   x86/mm: Provide untagged_addr() helper
>   x86/uaccess: Remove tags from the address before checking
>   x86/mm: Handle tagged memory accesses from kernel threads
>   x86/mm: Make LAM_U48 and mappings above 47-bits mutually exclusive
>   x86/mm: Implement PR_SET/GET_TAGGED_ADDR_CTRL with LAM
>
>  arch/arm64/include/asm/processor.h            |  12 +-
>  arch/arm64/kernel/process.c                   |  45 +++++-
>  arch/arm64/kernel/ptrace.c                    |   4 +-
>  arch/x86/include/asm/cpufeatures.h            |   1 +
>  arch/x86/include/asm/elf.h                    |   3 +-
>  arch/x86/include/asm/mmu.h                    |   1 +
>  arch/x86/include/asm/mmu_context.h            |  13 ++
>  arch/x86/include/asm/page_32.h                |   3 +
>  arch/x86/include/asm/page_64.h                |  19 +++
>  arch/x86/include/asm/processor-flags.h        |   2 +-
>  arch/x86/include/asm/processor.h              |  10 ++
>  arch/x86/include/asm/thread_info.h            |   9 +-
>  arch/x86/include/asm/tlbflush.h               |   5 +
>  arch/x86/include/asm/uaccess.h                |  16 +-
>  arch/x86/include/uapi/asm/processor-flags.h   |   6 +
>  arch/x86/kernel/process_64.c                  | 145 ++++++++++++++++++
>  arch/x86/kernel/sys_x86_64.c                  |   5 +-
>  arch/x86/mm/hugetlbpage.c                     |   6 +-
>  arch/x86/mm/mmap.c                            |   9 +-
>  arch/x86/mm/tlb.c                             | 124 +++++++++++++--
>  kernel/sys.c                                  |  14 +-
>  .../testing/selftests/arm64/tags/tags_test.c  |  31 ----
>  .../selftests/{arm64 => vm}/tags/.gitignore   |   0
>  .../selftests/{arm64 => vm}/tags/Makefile     |   0
>  .../{arm64 => vm}/tags/run_tags_test.sh       |   0
>  tools/testing/selftests/vm/tags/tags_test.c   |  57 +++++++
>  26 files changed, 464 insertions(+), 76 deletions(-)
>  delete mode 100644 tools/testing/selftests/arm64/tags/tags_test.c
>  rename tools/testing/selftests/{arm64 => vm}/tags/.gitignore (100%)
>  rename tools/testing/selftests/{arm64 => vm}/tags/Makefile (100%)
>  rename tools/testing/selftests/{arm64 => vm}/tags/run_tags_test.sh (100%)
>  create mode 100644 tools/testing/selftests/vm/tags/tags_test.c
>
> --
> 2.26.2
>