[PATCH v2 0/7] KVM: arm64: permit MAP_SHARED mappings with MTE enabled

[Peter Collingbourne]

Hi,

This patch series allows VMMs to use shared mappings in MTE enabled
guests. The first four patches are based on the series that Catalin sent
out, whose cover letter [1] I quote from below:

> This series aims to fix the races between initialising the tags on a
> page and setting the PG_mte_tagged flag. Currently the flag is set
> either before or after that tag initialisation and this can lead to CoW
> copying stale tags. The first patch moves the flag setting after the
> tags have been initialised, solving the CoW issue. However, concurrent
> mprotect() on a shared mapping may (very rarely) lead to valid tags
> being zeroed.
>
> The second skips the sanitise_mte_tags() call in kvm_set_spte_gfn(),
> deferring it to user_mem_abort(). The outcome is that no
> sanitise_mte_tags() can be simplified to skip the pfn_to_online_page()
> check and only rely on VM_MTE_ALLOWED vma flag that can be checked in
> user_mem_abort().
>
> The third and fourth patches use PG_arch_3 as a lock for page tagging,
> based on Peter Collingbourne's idea of a two-bit lock.
>
> I think the first patch can be queued but the rest needs some in depth
> review and test. With this series (if correct) we could allos MAP_SHARED
> on KVM guest memory but this is to be discussed separately as there are
> some KVM ABI implications.

I rebased Catalin's series onto -next, addressed the issues that I
identified in the review and added the proposed userspace enablement
patches after the series.

[1] https://lore.kernel.org/all/20220705142619.4135905-1-catalin.marinas@arm.com/

Catalin Marinas (3):
  arm64: mte: Fix/clarify the PG_mte_tagged semantics
  KVM: arm64: Simplify the sanitise_mte_tags() logic
  arm64: mte: Lock a page for MTE tag initialisation

Peter Collingbourne (4):
  mm: Add PG_arch_3 page flag
  KVM: arm64: unify the tests for VMAs in memslots when MTE is enabled
  KVM: arm64: permit all VM_MTE_ALLOWED mappings with MTE enabled
  Documentation: document the ABI changes for KVM_CAP_ARM_MTE

 Documentation/virt/kvm/api.rst   |  5 +--
 arch/arm64/include/asm/mte.h     | 62 ++++++++++++++++++++++++++++++++
 arch/arm64/include/asm/pgtable.h |  3 +-
 arch/arm64/kernel/cpufeature.c   |  4 ++-
 arch/arm64/kernel/elfcore.c      |  2 +-
 arch/arm64/kernel/hibernate.c    |  2 +-
 arch/arm64/kernel/mte.c          | 17 +++++----
 arch/arm64/kvm/guest.c           | 18 ++++++----
 arch/arm64/kvm/mmu.c             | 55 ++++++++++++----------------
 arch/arm64/mm/copypage.c         |  6 ++--
 arch/arm64/mm/fault.c            |  4 ++-
 arch/arm64/mm/mteswap.c          |  5 ++-
 fs/proc/page.c                   |  1 +
 include/linux/page-flags.h       |  1 +
 include/trace/events/mmflags.h   |  7 ++--
 mm/huge_memory.c                 |  1 +
 16 files changed, 134 insertions(+), 59 deletions(-)

-- 
2.37.1.359.gd136c6c3e2-goog