Messages in this thread |  | | From | Steven Price <> | | Subject | [PATCH v12 0/8] MTE support for KVM guest | | Date | Mon, 17 May 2021 13:32:31 +0100 |
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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@arm.com/ [2] https://lore.kernel.org/r/20210514095001.13236-1-catalin.marinas@arm.com/ [3] https://lore.kernel.org/r/de812a02fd94a0dba07d43606bd893c564aa4528.1620849613.git.pcc@google.com/
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
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