[PATCH v3 0/7] KVM: arm64: permit MAP_SHARED mappings with MTE enabled

From: Peter Collingbourne <pcc@google.com>
To: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu
Cc: Peter Collingbourne <pcc@google.com>,
	Cornelia Huck <cohuck@redhat.com>,
	 Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	 Evgenii Stepanov <eugenis@google.com>,
	kvm@vger.kernel.org,  Steven Price <steven.price@arm.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>
Subject: [PATCH v3 0/7] KVM: arm64: permit MAP_SHARED mappings with MTE enabled
Date: Wed, 10 Aug 2022 12:30:26 -0700	[thread overview]
Message-ID: <20220810193033.1090251-1-pcc@google.com> (raw)

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/kernel-page-flags.h |  1 +
 include/linux/page-flags.h        |  1 +
 include/trace/events/mmflags.h    |  7 ++--
 mm/huge_memory.c                  |  1 +
 tools/vm/page-types.c             |  2 +
 18 files changed, 137 insertions(+), 59 deletions(-)

-- 
2.37.1.559.g78731f0fdb-goog

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