[PATCH v12 0/8] MTE support for KVM guest

[Steven Price]

This series adds support for using the Arm Memory Tagging Extensions
(MTE) in a KVM guest.

Changes since v11[1]:

 * Series is prefixed with a bug fix for a potential race synchronising
   tags. This is basically race as was recently[2] fixed for
   PG_dcache_clean where the update of the page flag cannot be done
   atomically with the work that flag represents.

   For the PG_dcache_clean case the problem is easier because extra
   cache maintenance isn't a problem, but here restoring the tags twice
   could cause data loss.

   The current solution is a global spinlock for mte_sync_page_tags().
   If we hit scalability problems that other solutions such as
   potentially using another page flag as a lock will need to be
   investigated.

 * The second patch is from Catalin to mitigate the performance impact
   of the first - by handling the page zeroing case explicitly we can
   avoid entering mte_sync_page_tags() at all in most cases. Peter
   Collingbourne has a patch which similarly improves this case using
   the DC GZVA instruction. So this patch may be dropped in favour of
   Peter's, however Catalin's is likely easier to backport.

 * Use pte_access_permitted() in set_pte_at() to identify pages which
   may be accessed by the user rather than open-coding a check for
   PTE_USER. Also add a comment documenting what's going on.
   There's also some short-cuts added in mte_sync_tags() compared to the
   previous post, to again mitigate the performance impact of the first
   patch.

 * Move the code to sanitise tags out of user_mem_abort() into its own
   function. Also call this new function from kvm_set_spte_gfn() as that
   path was missing the sanitising.

   Originally I was going to move the code all the way down to
   kvm_pgtable_stage2_map(). Sadly as that also part of the EL2
   hypervisor this breaks nVHE as the code needs to perform actions in
   the host.

 * Drop the union in struct kvm_vcpu_events - it served no purpose and
   was confusing.

 * Update CAP number (again) and other minor conflict resolutions.

[1] https://lore.kernel.org/r/20210416154309.22129-1-steven.price@xxxxxxx/
[2] https://lore.kernel.org/r/20210514095001.13236-1-catalin.marinas@xxxxxxx/
[3] https://lore.kernel.org/r/de812a02fd94a0dba07d43606bd893c564aa4528.1620849613.git.pcc@xxxxxxxxxx/

Catalin Marinas (1):
  arm64: Handle MTE tags zeroing in __alloc_zeroed_user_highpage()

Steven Price (7):
  arm64: mte: Handle race when synchronising tags
  arm64: mte: Sync tags for pages where PTE is untagged
  arm64: kvm: Introduce MTE VM feature
  arm64: kvm: Save/restore MTE registers
  arm64: kvm: Expose KVM_ARM_CAP_MTE
  KVM: arm64: ioctl to fetch/store tags in a guest
  KVM: arm64: Document MTE capability and ioctl

 Documentation/virt/kvm/api.rst             | 53 +++++++++++++++
 arch/arm64/include/asm/kvm_emulate.h       |  3 +
 arch/arm64/include/asm/kvm_host.h          |  9 +++
 arch/arm64/include/asm/kvm_mte.h           | 66 ++++++++++++++++++
 arch/arm64/include/asm/page.h              |  6 +-
 arch/arm64/include/asm/pgtable.h           |  9 ++-
 arch/arm64/include/asm/sysreg.h            |  3 +-
 arch/arm64/include/uapi/asm/kvm.h          | 11 +++
 arch/arm64/kernel/asm-offsets.c            |  3 +
 arch/arm64/kernel/mte.c                    | 37 ++++++++--
 arch/arm64/kvm/arm.c                       | 78 ++++++++++++++++++++++
 arch/arm64/kvm/hyp/entry.S                 |  7 ++
 arch/arm64/kvm/hyp/exception.c             |  3 +-
 arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 21 ++++++
 arch/arm64/kvm/mmu.c                       | 37 +++++++++-
 arch/arm64/kvm/sys_regs.c                  | 28 ++++++--
 arch/arm64/mm/fault.c                      | 21 ++++++
 include/uapi/linux/kvm.h                   |  2 +
 18 files changed, 381 insertions(+), 16 deletions(-)
 create mode 100644 arch/arm64/include/asm/kvm_mte.h

-- 
2.20.1