Hi,
This patch series allows VMMs to use shared mappings in MTE enabled
guests. The first five patches were taken from Catalin's tree [1] which
addressed some review feedback from when they were previously sent out
as v3 of this series. The first patch from Catalin's tree makes room
for an additional PG_arch_3 flag by making the newer PG_arch_* flags
arch-dependent. The next four patches are based on a series that
Catalin sent out prior to v3, whose cover letter [2] 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.
In this v5 I rebased Catalin's tree onto -next again. Please double check
my rebase, which resolved the conflict with commit a8e5e5146ad0 ("arm64:
mte: Avoid setting PG_mte_tagged if no tags cleared or restored").
I now have Reviewed-by for all patches except for the last one, which adds
the documentation. Thanks for the reviews so far, and please take a look!
I've tested it on QEMU as well as on MTE-capable hardware by booting a
Linux kernel and userspace under a crosvm with MTE support [3].
[1] git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux devel/mte-pg-flags
[2] https://lore.kernel.org/all/20220705142619.4135905-1-catalin.marinas@xxxxxxx/
[3] https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3892141
Catalin Marinas (4):
mm: Do not enable PG_arch_2 for all 64-bit architectures
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/Kconfig | 1 +
arch/arm64/include/asm/mte.h | 65 ++++++++++++++++++++++++++++++-
arch/arm64/include/asm/pgtable.h | 4 +-
arch/arm64/kernel/cpufeature.c | 4 +-
arch/arm64/kernel/elfcore.c | 2 +-
arch/arm64/kernel/hibernate.c | 2 +-
arch/arm64/kernel/mte.c | 21 +++++-----
arch/arm64/kvm/guest.c | 18 +++++----
arch/arm64/kvm/mmu.c | 55 +++++++++++---------------
arch/arm64/mm/copypage.c | 7 +++-
arch/arm64/mm/fault.c | 4 +-
arch/arm64/mm/mteswap.c | 16 +++-----
fs/proc/page.c | 3 +-
include/linux/kernel-page-flags.h | 1 +
include/linux/page-flags.h | 3 +-
include/trace/events/mmflags.h | 9 +++--
mm/Kconfig | 8 ++++
mm/huge_memory.c | 3 +-
19 files changed, 152 insertions(+), 79 deletions(-)
--
2.38.1.431.g37b22c650d-goog
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