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@xxxxxxx/ 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
